diff --git a/.eslintrc.json b/.eslintrc.json
index 7d1cf6ad91..e94d64e56b 100644
--- a/.eslintrc.json
+++ b/.eslintrc.json
@@ -7,7 +7,7 @@
     "parser": "babel-eslint",
     "parserOptions": {
         "warnOnUnsupportedTypeScriptVersion": false,
-        "sourceType": "module"
+        "sourceType": "unambiguous"
     },
     "plugins": ["eslint-plugin-empty-returns"],
     "rules": {
@@ -29,6 +29,7 @@
                 "newlines-between": "always"
             }
         ],
+        "import/unambiguous": "error",
         "new-cap": [
             "error",
             {
@@ -88,7 +89,7 @@
         ],
         "radix": "error",
         "spaced-comment": "off",
-        "strict": "off",
+        "strict": "error",
         "valid-typeof": ["error", {"requireStringLiterals": true}],
         "yoda": "error"
     },
@@ -331,6 +332,12 @@
                 "@typescript-eslint/unified-signatures": "error"
             }
         },
+        {
+            "files": ["**/*.d.ts"],
+            "rules": {
+                "import/unambiguous": "off"
+            }
+        },
         {
             "files": ["frontend_tests/**"],
             "globals": {
diff --git a/babel.config.js b/babel.config.js
index 889341cc91..642e5ac477 100644
--- a/babel.config.js
+++ b/babel.config.js
@@ -1,3 +1,5 @@
+"use strict";
+
 module.exports = {
     presets: [
         [
diff --git a/frontend_tests/casper_lib/common.js b/frontend_tests/casper_lib/common.js
index 62b9c0cd52..b61d3634ca 100644
--- a/frontend_tests/casper_lib/common.js
+++ b/frontend_tests/casper_lib/common.js
@@ -1,3 +1,5 @@
+"use strict";
+
 var util = require("util");
 
 var test_credentials = require("../../var/casper/test_credentials.js").test_credentials;
diff --git a/frontend_tests/casper_lib/polyfill.js b/frontend_tests/casper_lib/polyfill.js
index 62cd4a5047..35de4557bb 100644
--- a/frontend_tests/casper_lib/polyfill.js
+++ b/frontend_tests/casper_lib/polyfill.js
@@ -1,3 +1,5 @@
+"use strict";
+
 /* eslint-env browser */
 
 // PhantomJS doesn’t support new DOMParser().parseFromString(…, "text/html").
diff --git a/frontend_tests/casper_tests/00-realm-creation.js b/frontend_tests/casper_tests/00-realm-creation.js
index fb299ad3fc..5816df80c0 100644
--- a/frontend_tests/casper_tests/00-realm-creation.js
+++ b/frontend_tests/casper_tests/00-realm-creation.js
@@ -1,3 +1,5 @@
+"use strict";
+
 var common = require("../casper_lib/common.js");
 
 var email = "alice@test.example.com";
diff --git a/frontend_tests/casper_tests/01-login.js b/frontend_tests/casper_tests/01-login.js
index b10249c05c..6fca4a4d97 100644
--- a/frontend_tests/casper_tests/01-login.js
+++ b/frontend_tests/casper_tests/01-login.js
@@ -1,3 +1,5 @@
+"use strict";
+
 var common = require("../casper_lib/common.js");
 
 var realm_url = "http://zulip.zulipdev.com:9981/";
diff --git a/frontend_tests/casper_tests/02-site.js b/frontend_tests/casper_tests/02-site.js
index 37510c14cd..9f58ceae8c 100644
--- a/frontend_tests/casper_tests/02-site.js
+++ b/frontend_tests/casper_tests/02-site.js
@@ -1,3 +1,5 @@
+"use strict";
+
 /* Script for testing the web client.
 
    This runs under CasperJS.  It's an end-to-end black-box sort of test.  It
diff --git a/frontend_tests/casper_tests/03-narrow.js b/frontend_tests/casper_tests/03-narrow.js
index 180b305446..ecf8e464b3 100644
--- a/frontend_tests/casper_tests/03-narrow.js
+++ b/frontend_tests/casper_tests/03-narrow.js
@@ -1,3 +1,5 @@
+"use strict";
+
 var common = require("../casper_lib/common.js");
 
 common.start_and_log_in();
diff --git a/frontend_tests/casper_tests/04-compose.js b/frontend_tests/casper_tests/04-compose.js
index 3ffb1d51d7..cfe40f760a 100644
--- a/frontend_tests/casper_tests/04-compose.js
+++ b/frontend_tests/casper_tests/04-compose.js
@@ -1,3 +1,5 @@
+"use strict";
+
 var common = require("../casper_lib/common.js");
 
 common.start_and_log_in();
diff --git a/frontend_tests/casper_tests/05-subscriptions.js b/frontend_tests/casper_tests/05-subscriptions.js
index f30847a1ad..d4a4609764 100644
--- a/frontend_tests/casper_tests/05-subscriptions.js
+++ b/frontend_tests/casper_tests/05-subscriptions.js
@@ -1,3 +1,5 @@
+"use strict";
+
 var common = require("../casper_lib/common.js");
 
 function stream_checkbox(stream_name) {
diff --git a/frontend_tests/casper_tests/06-settings.js b/frontend_tests/casper_tests/06-settings.js
index aca1fc473f..75b215513b 100644
--- a/frontend_tests/casper_tests/06-settings.js
+++ b/frontend_tests/casper_tests/06-settings.js
@@ -1,3 +1,5 @@
+"use strict";
+
 var test_credentials = require("../../var/casper/test_credentials.js").test_credentials;
 var common = require("../casper_lib/common.js");
 
diff --git a/frontend_tests/casper_tests/07-stars.js b/frontend_tests/casper_tests/07-stars.js
index 79e05f474b..e3028116bc 100644
--- a/frontend_tests/casper_tests/07-stars.js
+++ b/frontend_tests/casper_tests/07-stars.js
@@ -1,3 +1,5 @@
+"use strict";
+
 var common = require("../casper_lib/common.js");
 
 function star_count() {
diff --git a/frontend_tests/casper_tests/08-edit.js b/frontend_tests/casper_tests/08-edit.js
index 700ec1bf60..2639e21d80 100644
--- a/frontend_tests/casper_tests/08-edit.js
+++ b/frontend_tests/casper_tests/08-edit.js
@@ -1,3 +1,5 @@
+"use strict";
+
 var common = require("../casper_lib/common.js");
 
 casper.options.verbose = true;
diff --git a/frontend_tests/casper_tests/09-navigation.js b/frontend_tests/casper_tests/09-navigation.js
index 98e629fe66..69ad9d7fc0 100644
--- a/frontend_tests/casper_tests/09-navigation.js
+++ b/frontend_tests/casper_tests/09-navigation.js
@@ -1,3 +1,5 @@
+"use strict";
+
 var common = require("../casper_lib/common.js");
 
 // Test basic tab navigation.
diff --git a/frontend_tests/casper_tests/10-admin.js b/frontend_tests/casper_tests/10-admin.js
index 17c3d118b1..357f8ac986 100644
--- a/frontend_tests/casper_tests/10-admin.js
+++ b/frontend_tests/casper_tests/10-admin.js
@@ -1,3 +1,5 @@
+"use strict";
+
 var common = require("../casper_lib/common.js");
 
 common.start_and_log_in();
diff --git a/frontend_tests/casper_tests/11-mention.js b/frontend_tests/casper_tests/11-mention.js
index 57a848f116..7286409183 100644
--- a/frontend_tests/casper_tests/11-mention.js
+++ b/frontend_tests/casper_tests/11-mention.js
@@ -1,3 +1,5 @@
+"use strict";
+
 var common = require("../casper_lib/common.js");
 
 common.start_and_log_in();
diff --git a/frontend_tests/casper_tests/12-custom-profile.js b/frontend_tests/casper_tests/12-custom-profile.js
index 659888d96b..4c0d98eb3b 100644
--- a/frontend_tests/casper_tests/12-custom-profile.js
+++ b/frontend_tests/casper_tests/12-custom-profile.js
@@ -1,3 +1,5 @@
+"use strict";
+
 var common = require("../casper_lib/common.js");
 
 common.start_and_log_in();
diff --git a/frontend_tests/casper_tests/13-user-deactivation.js b/frontend_tests/casper_tests/13-user-deactivation.js
index cdb15ccd48..b3b719b87c 100644
--- a/frontend_tests/casper_tests/13-user-deactivation.js
+++ b/frontend_tests/casper_tests/13-user-deactivation.js
@@ -1,3 +1,5 @@
+"use strict";
+
 var common = require("../casper_lib/common.js");
 
 function user_row(name) {
diff --git a/frontend_tests/casper_tests/14-drafts.js b/frontend_tests/casper_tests/14-drafts.js
index 46aed73317..485d5f7999 100644
--- a/frontend_tests/casper_tests/14-drafts.js
+++ b/frontend_tests/casper_tests/14-drafts.js
@@ -1,3 +1,5 @@
+"use strict";
+
 var common = require("../casper_lib/common.js");
 
 function waitWhileDraftsVisible(then) {
diff --git a/frontend_tests/casper_tests/15-delete-message.js b/frontend_tests/casper_tests/15-delete-message.js
index 10814cf8ba..c657cd0c4b 100644
--- a/frontend_tests/casper_tests/15-delete-message.js
+++ b/frontend_tests/casper_tests/15-delete-message.js
@@ -1,3 +1,5 @@
+"use strict";
+
 var common = require("../casper_lib/common.js");
 
 common.start_and_log_in();
diff --git a/frontend_tests/casper_tests/16-copy-and-paste.js b/frontend_tests/casper_tests/16-copy-and-paste.js
index f600fedba0..8032fd23ec 100644
--- a/frontend_tests/casper_tests/16-copy-and-paste.js
+++ b/frontend_tests/casper_tests/16-copy-and-paste.js
@@ -1,3 +1,5 @@
+"use strict";
+
 var common = require("../casper_lib/common.js");
 
 common.start_and_log_in();
diff --git a/frontend_tests/casper_tests/17-realm-linkifier.js b/frontend_tests/casper_tests/17-realm-linkifier.js
index a2d5f45273..2ea74c563f 100644
--- a/frontend_tests/casper_tests/17-realm-linkifier.js
+++ b/frontend_tests/casper_tests/17-realm-linkifier.js
@@ -1,3 +1,5 @@
+"use strict";
+
 var common = require("../casper_lib/common.js");
 
 common.start_and_log_in();
diff --git a/frontend_tests/node_tests/activity.js b/frontend_tests/node_tests/activity.js
index ae139374b9..200f7cf8c6 100644
--- a/frontend_tests/node_tests/activity.js
+++ b/frontend_tests/node_tests/activity.js
@@ -1,3 +1,5 @@
+"use strict";
+
 set_global("$", global.make_zjquery());
 const window_stub = $.create("window-stub");
 set_global("to_$", () => window_stub);
diff --git a/frontend_tests/node_tests/alert_words.js b/frontend_tests/node_tests/alert_words.js
index 1ddd1a2bc7..345e127860 100644
--- a/frontend_tests/node_tests/alert_words.js
+++ b/frontend_tests/node_tests/alert_words.js
@@ -1,3 +1,5 @@
+"use strict";
+
 const params = {
     alert_words: ["alertone", "alerttwo", "alertthree", "al*rt.*s", ".+", "emoji"],
 };
diff --git a/frontend_tests/node_tests/alert_words_ui.js b/frontend_tests/node_tests/alert_words_ui.js
index 6993dae0ae..4f65657666 100644
--- a/frontend_tests/node_tests/alert_words_ui.js
+++ b/frontend_tests/node_tests/alert_words_ui.js
@@ -1,3 +1,5 @@
+"use strict";
+
 set_global("$", global.make_zjquery());
 
 set_global("channel", {});
diff --git a/frontend_tests/node_tests/billing.js b/frontend_tests/node_tests/billing.js
index 49a5d58405..5dba519f68 100644
--- a/frontend_tests/node_tests/billing.js
+++ b/frontend_tests/node_tests/billing.js
@@ -1,3 +1,5 @@
+"use strict";
+
 const noop = () => {};
 const fs = require("fs");
 
diff --git a/frontend_tests/node_tests/billing_helpers.js b/frontend_tests/node_tests/billing_helpers.js
index 592dea39a3..cb439fbf0a 100644
--- a/frontend_tests/node_tests/billing_helpers.js
+++ b/frontend_tests/node_tests/billing_helpers.js
@@ -1,3 +1,5 @@
+"use strict";
+
 const fs = require("fs");
 
 const JQuery = require("jquery");
diff --git a/frontend_tests/node_tests/blueslip_stacktrace.js b/frontend_tests/node_tests/blueslip_stacktrace.js
index 79d1d0ed03..fb99707110 100644
--- a/frontend_tests/node_tests/blueslip_stacktrace.js
+++ b/frontend_tests/node_tests/blueslip_stacktrace.js
@@ -1,3 +1,5 @@
+"use strict";
+
 const blueslip_stacktrace = zrequire("blueslip_stacktrace");
 
 run_test("clean_path", () => {
diff --git a/frontend_tests/node_tests/bot_data.js b/frontend_tests/node_tests/bot_data.js
index 4d058208c3..46a20964a6 100644
--- a/frontend_tests/node_tests/bot_data.js
+++ b/frontend_tests/node_tests/bot_data.js
@@ -1,3 +1,5 @@
+"use strict";
+
 const _settings_bots = {
     render_bots: () => {},
 };
diff --git a/frontend_tests/node_tests/buddy_data.js b/frontend_tests/node_tests/buddy_data.js
index 01b761ec8c..145ee86f4a 100644
--- a/frontend_tests/node_tests/buddy_data.js
+++ b/frontend_tests/node_tests/buddy_data.js
@@ -1,3 +1,5 @@
+"use strict";
+
 const _ = require("lodash");
 
 const _page_params = {};
diff --git a/frontend_tests/node_tests/buddy_list.js b/frontend_tests/node_tests/buddy_list.js
index c394c986b2..bd346d6619 100644
--- a/frontend_tests/node_tests/buddy_list.js
+++ b/frontend_tests/node_tests/buddy_list.js
@@ -1,3 +1,5 @@
+"use strict";
+
 const _ = require("lodash");
 
 set_global("$", global.make_zjquery());
diff --git a/frontend_tests/node_tests/channel.js b/frontend_tests/node_tests/channel.js
index b8bb5ef39d..124b1ba14d 100644
--- a/frontend_tests/node_tests/channel.js
+++ b/frontend_tests/node_tests/channel.js
@@ -1,3 +1,5 @@
+"use strict";
+
 const _ = require("lodash");
 
 set_global("$", {});
diff --git a/frontend_tests/node_tests/color_data.js b/frontend_tests/node_tests/color_data.js
index e5e484d7b5..b09974b90b 100644
--- a/frontend_tests/node_tests/color_data.js
+++ b/frontend_tests/node_tests/color_data.js
@@ -1,3 +1,5 @@
+"use strict";
+
 zrequire("color_data");
 
 run_test("pick_color", () => {
diff --git a/frontend_tests/node_tests/colorspace.js b/frontend_tests/node_tests/colorspace.js
index b8d1c5a930..28026853de 100644
--- a/frontend_tests/node_tests/colorspace.js
+++ b/frontend_tests/node_tests/colorspace.js
@@ -1,3 +1,5 @@
+"use strict";
+
 zrequire("colorspace");
 
 run_test("sRGB_to_linear", () => {
diff --git a/frontend_tests/node_tests/common.js b/frontend_tests/node_tests/common.js
index 24fb9ea3b4..f9d7a0918c 100644
--- a/frontend_tests/node_tests/common.js
+++ b/frontend_tests/node_tests/common.js
@@ -1,3 +1,5 @@
+"use strict";
+
 const noop = () => {};
 
 set_global("$", global.make_zjquery());
diff --git a/frontend_tests/node_tests/components.js b/frontend_tests/node_tests/components.js
index 18b82a5799..40d2ed7411 100644
--- a/frontend_tests/node_tests/components.js
+++ b/frontend_tests/node_tests/components.js
@@ -1,3 +1,5 @@
+"use strict";
+
 const _ = require("lodash");
 
 zrequire("keydown_util");
diff --git a/frontend_tests/node_tests/compose.js b/frontend_tests/node_tests/compose.js
index e663ad2dee..f0863e8bf6 100644
--- a/frontend_tests/node_tests/compose.js
+++ b/frontend_tests/node_tests/compose.js
@@ -1,3 +1,5 @@
+"use strict";
+
 const {JSDOM} = require("jsdom");
 const rewiremock = require("rewiremock/node");
 
diff --git a/frontend_tests/node_tests/compose_actions.js b/frontend_tests/node_tests/compose_actions.js
index 83bdc82745..de62823d54 100644
--- a/frontend_tests/node_tests/compose_actions.js
+++ b/frontend_tests/node_tests/compose_actions.js
@@ -1,3 +1,5 @@
+"use strict";
+
 const noop = function () {};
 const return_false = function () {
     return false;
diff --git a/frontend_tests/node_tests/compose_fade.js b/frontend_tests/node_tests/compose_fade.js
index 2997db0834..33a60d2b9a 100644
--- a/frontend_tests/node_tests/compose_fade.js
+++ b/frontend_tests/node_tests/compose_fade.js
@@ -1,3 +1,5 @@
+"use strict";
+
 zrequire("stream_data");
 zrequire("people");
 zrequire("compose_fade");
diff --git a/frontend_tests/node_tests/compose_pm_pill.js b/frontend_tests/node_tests/compose_pm_pill.js
index a58db08172..d13a954408 100644
--- a/frontend_tests/node_tests/compose_pm_pill.js
+++ b/frontend_tests/node_tests/compose_pm_pill.js
@@ -1,3 +1,5 @@
+"use strict";
+
 set_global("$", global.make_zjquery());
 
 const _people = {
diff --git a/frontend_tests/node_tests/compose_ui.js b/frontend_tests/node_tests/compose_ui.js
index 0eb1b2a747..1605963029 100644
--- a/frontend_tests/node_tests/compose_ui.js
+++ b/frontend_tests/node_tests/compose_ui.js
@@ -1,3 +1,5 @@
+"use strict";
+
 zrequire("compose_ui");
 zrequire("people");
 zrequire("user_status");
diff --git a/frontend_tests/node_tests/composebox_typeahead.js b/frontend_tests/node_tests/composebox_typeahead.js
index 2b4ccec0a4..58713b5f02 100644
--- a/frontend_tests/node_tests/composebox_typeahead.js
+++ b/frontend_tests/node_tests/composebox_typeahead.js
@@ -1,3 +1,5 @@
+"use strict";
+
 const emoji = zrequire("emoji", "shared/js/emoji");
 const typeahead = zrequire("typeahead", "shared/js/typeahead");
 zrequire("compose_state");
diff --git a/frontend_tests/node_tests/copy_and_paste.js b/frontend_tests/node_tests/copy_and_paste.js
index cb9789c6fd..1cb65caeb7 100644
--- a/frontend_tests/node_tests/copy_and_paste.js
+++ b/frontend_tests/node_tests/copy_and_paste.js
@@ -1,3 +1,5 @@
+"use strict";
+
 global.stub_out_jquery();
 
 set_global("page_params", {
diff --git a/frontend_tests/node_tests/dispatch.js b/frontend_tests/node_tests/dispatch.js
index b9bc1429fd..1135ade319 100644
--- a/frontend_tests/node_tests/dispatch.js
+++ b/frontend_tests/node_tests/dispatch.js
@@ -1,3 +1,5 @@
+"use strict";
+
 const noop = function () {};
 
 const events = require("./lib/events.js");
diff --git a/frontend_tests/node_tests/dispatch_subs.js b/frontend_tests/node_tests/dispatch_subs.js
index 90286fa9e0..36b3b9f4a8 100644
--- a/frontend_tests/node_tests/dispatch_subs.js
+++ b/frontend_tests/node_tests/dispatch_subs.js
@@ -1,3 +1,5 @@
+"use strict";
+
 const events = require("./lib/events.js");
 
 const event_fixtures = events.fixtures;
diff --git a/frontend_tests/node_tests/drafts.js b/frontend_tests/node_tests/drafts.js
index 5e03fb09e1..2a433129cf 100644
--- a/frontend_tests/node_tests/drafts.js
+++ b/frontend_tests/node_tests/drafts.js
@@ -1,3 +1,5 @@
+"use strict";
+
 const XDate = require("xdate");
 
 set_global("$", global.make_zjquery());
diff --git a/frontend_tests/node_tests/dropdown_list_widget.js b/frontend_tests/node_tests/dropdown_list_widget.js
index 36d1d3e8bc..afd13e89a6 100644
--- a/frontend_tests/node_tests/dropdown_list_widget.js
+++ b/frontend_tests/node_tests/dropdown_list_widget.js
@@ -1,3 +1,5 @@
+"use strict";
+
 zrequire("dropdown_list_widget");
 zrequire("scroll_util");
 set_global("$", global.make_zjquery());
diff --git a/frontend_tests/node_tests/echo.js b/frontend_tests/node_tests/echo.js
index 22f1ceaf1c..a38c24862f 100644
--- a/frontend_tests/node_tests/echo.js
+++ b/frontend_tests/node_tests/echo.js
@@ -1,3 +1,5 @@
+"use strict";
+
 set_global("$", global.make_zjquery());
 set_global("markdown", {});
 set_global("local_message", {
diff --git a/frontend_tests/node_tests/emoji.js b/frontend_tests/node_tests/emoji.js
index 48f2167c16..ac0567253a 100644
--- a/frontend_tests/node_tests/emoji.js
+++ b/frontend_tests/node_tests/emoji.js
@@ -1,3 +1,5 @@
+"use strict";
+
 const emoji_codes = zrequire("emoji_codes", "generated/emoji/emoji_codes.json");
 
 const events = require("./lib/events.js");
diff --git a/frontend_tests/node_tests/emoji_picker.js b/frontend_tests/node_tests/emoji_picker.js
index 7b7e4c8600..88f6247e4f 100644
--- a/frontend_tests/node_tests/emoji_picker.js
+++ b/frontend_tests/node_tests/emoji_picker.js
@@ -1,3 +1,5 @@
+"use strict";
+
 const _ = require("lodash");
 
 const emoji = zrequire("emoji", "shared/js/emoji");
diff --git a/frontend_tests/node_tests/fenced_code.js b/frontend_tests/node_tests/fenced_code.js
index 75dace8597..5d90ab2369 100644
--- a/frontend_tests/node_tests/fenced_code.js
+++ b/frontend_tests/node_tests/fenced_code.js
@@ -1,3 +1,5 @@
+"use strict";
+
 const fenced_code = zrequire("fenced_code", "shared/js/fenced_code");
 
 run_test("get_unused_fence", () => {
diff --git a/frontend_tests/node_tests/fetch_status.js b/frontend_tests/node_tests/fetch_status.js
index 82304e1883..3ae0437b70 100644
--- a/frontend_tests/node_tests/fetch_status.js
+++ b/frontend_tests/node_tests/fetch_status.js
@@ -1,3 +1,5 @@
+"use strict";
+
 const FetchStatus = zrequire("fetch_status");
 set_global("message_scroll", {
     hide_loading_older: () => {},
diff --git a/frontend_tests/node_tests/filter.js b/frontend_tests/node_tests/filter.js
index 6247f8477b..a77a828b5f 100644
--- a/frontend_tests/node_tests/filter.js
+++ b/frontend_tests/node_tests/filter.js
@@ -1,3 +1,5 @@
+"use strict";
+
 zrequire("unread");
 zrequire("stream_data");
 zrequire("people");
diff --git a/frontend_tests/node_tests/fold_dict.js b/frontend_tests/node_tests/fold_dict.js
index 7be296a120..7df4c48efb 100644
--- a/frontend_tests/node_tests/fold_dict.js
+++ b/frontend_tests/node_tests/fold_dict.js
@@ -1,3 +1,5 @@
+"use strict";
+
 const FoldDict = zrequire("fold_dict").FoldDict;
 
 run_test("basic", () => {
diff --git a/frontend_tests/node_tests/general.js b/frontend_tests/node_tests/general.js
index e64e0b7749..c2b13aa50d 100644
--- a/frontend_tests/node_tests/general.js
+++ b/frontend_tests/node_tests/general.js
@@ -1,3 +1,5 @@
+"use strict";
+
 // This is a general tour of how to write node tests that
 // may also give you some quick insight on how the Zulip
 // browser app is constructed.  Let's start with testing
diff --git a/frontend_tests/node_tests/hash_util.js b/frontend_tests/node_tests/hash_util.js
index b0e3dd3264..47369be8b2 100644
--- a/frontend_tests/node_tests/hash_util.js
+++ b/frontend_tests/node_tests/hash_util.js
@@ -1,3 +1,5 @@
+"use strict";
+
 zrequire("hash_util");
 zrequire("stream_data");
 zrequire("people");
diff --git a/frontend_tests/node_tests/hashchange.js b/frontend_tests/node_tests/hashchange.js
index 36987c07ea..b67a468477 100644
--- a/frontend_tests/node_tests/hashchange.js
+++ b/frontend_tests/node_tests/hashchange.js
@@ -1,3 +1,5 @@
+"use strict";
+
 set_global("$", global.make_zjquery());
 const window_stub = $.create("window-stub");
 set_global("location", {
diff --git a/frontend_tests/node_tests/hotkey.js b/frontend_tests/node_tests/hotkey.js
index 0243a84dcc..ffa35bea2f 100644
--- a/frontend_tests/node_tests/hotkey.js
+++ b/frontend_tests/node_tests/hotkey.js
@@ -1,3 +1,5 @@
+"use strict";
+
 // Important note on these tests:
 //
 // The way the Zulip hotkey tests work is as follows.  First, we set
diff --git a/frontend_tests/node_tests/i18n.js b/frontend_tests/node_tests/i18n.js
index 23616fee5c..41ce76eb8e 100644
--- a/frontend_tests/node_tests/i18n.js
+++ b/frontend_tests/node_tests/i18n.js
@@ -1,3 +1,5 @@
+"use strict";
+
 zrequire("templates");
 
 // We download our translations in `page_params` (which
diff --git a/frontend_tests/node_tests/input_pill.js b/frontend_tests/node_tests/input_pill.js
index 15a75308b1..3bc4694ec8 100644
--- a/frontend_tests/node_tests/input_pill.js
+++ b/frontend_tests/node_tests/input_pill.js
@@ -1,3 +1,5 @@
+"use strict";
+
 set_global("$", global.make_zjquery());
 zrequire("input_pill");
 
diff --git a/frontend_tests/node_tests/keydown_util.js b/frontend_tests/node_tests/keydown_util.js
index 221753b04d..274612723e 100644
--- a/frontend_tests/node_tests/keydown_util.js
+++ b/frontend_tests/node_tests/keydown_util.js
@@ -1,3 +1,5 @@
+"use strict";
+
 set_global("$", global.make_zjquery());
 
 zrequire("keydown_util");
diff --git a/frontend_tests/node_tests/lazy_set.js b/frontend_tests/node_tests/lazy_set.js
index 8e917715a9..b84fffce79 100644
--- a/frontend_tests/node_tests/lazy_set.js
+++ b/frontend_tests/node_tests/lazy_set.js
@@ -1,3 +1,5 @@
+"use strict";
+
 const LazySet = zrequire("lazy_set").LazySet;
 
 /*
diff --git a/frontend_tests/node_tests/lib/events.js b/frontend_tests/node_tests/lib/events.js
index 759dab34d0..9833ea2260 100644
--- a/frontend_tests/node_tests/lib/events.js
+++ b/frontend_tests/node_tests/lib/events.js
@@ -1,3 +1,5 @@
+"use strict";
+
 // TODO: These events are not guaranteed to be perfectly
 //       representative of what the server sends.  For
 //       now we just want very basic test coverage.  We
diff --git a/frontend_tests/node_tests/lightbox.js b/frontend_tests/node_tests/lightbox.js
index 202615c9df..e89251fbf5 100644
--- a/frontend_tests/node_tests/lightbox.js
+++ b/frontend_tests/node_tests/lightbox.js
@@ -1,3 +1,5 @@
+"use strict";
+
 zrequire("rows");
 zrequire("lightbox");
 
diff --git a/frontend_tests/node_tests/list_cursor.js b/frontend_tests/node_tests/list_cursor.js
index 9b8ecf1c10..d3ce3922c7 100644
--- a/frontend_tests/node_tests/list_cursor.js
+++ b/frontend_tests/node_tests/list_cursor.js
@@ -1,3 +1,5 @@
+"use strict";
+
 zrequire("list_cursor");
 
 run_test("config errors", () => {
diff --git a/frontend_tests/node_tests/list_render.js b/frontend_tests/node_tests/list_render.js
index 863bdef8b7..89435353dc 100644
--- a/frontend_tests/node_tests/list_render.js
+++ b/frontend_tests/node_tests/list_render.js
@@ -1,3 +1,5 @@
+"use strict";
+
 zrequire("list_render");
 
 // We need these stubs to get by instanceof checks.
diff --git a/frontend_tests/node_tests/markdown.js b/frontend_tests/node_tests/markdown.js
index 333b72ee97..94fd9fcef3 100644
--- a/frontend_tests/node_tests/markdown.js
+++ b/frontend_tests/node_tests/markdown.js
@@ -1,3 +1,5 @@
+"use strict";
+
 zrequire("hash_util");
 
 const emoji = zrequire("emoji", "shared/js/emoji");
diff --git a/frontend_tests/node_tests/markdown_katex.js b/frontend_tests/node_tests/markdown_katex.js
index 76e54e7102..0d301a030d 100644
--- a/frontend_tests/node_tests/markdown_katex.js
+++ b/frontend_tests/node_tests/markdown_katex.js
@@ -1,3 +1,5 @@
+"use strict";
+
 /*
     This whole module is dedicated to adding
     one line of coverage for markdown.js.
diff --git a/frontend_tests/node_tests/message_edit.js b/frontend_tests/node_tests/message_edit.js
index 1de52e0750..be132278ff 100644
--- a/frontend_tests/node_tests/message_edit.js
+++ b/frontend_tests/node_tests/message_edit.js
@@ -1,3 +1,5 @@
+"use strict";
+
 set_global("document", null);
 set_global("page_params", {
     realm_community_topic_editing_limit_seconds: 86400,
diff --git a/frontend_tests/node_tests/message_events.js b/frontend_tests/node_tests/message_events.js
index 4b867b1bc2..b29b64dda7 100644
--- a/frontend_tests/node_tests/message_events.js
+++ b/frontend_tests/node_tests/message_events.js
@@ -1,3 +1,5 @@
+"use strict";
+
 zrequire("message_events");
 zrequire("message_store");
 zrequire("muting");
diff --git a/frontend_tests/node_tests/message_fetch.js b/frontend_tests/node_tests/message_fetch.js
index 13bb9081bf..9230517ca1 100644
--- a/frontend_tests/node_tests/message_fetch.js
+++ b/frontend_tests/node_tests/message_fetch.js
@@ -1,3 +1,5 @@
+"use strict";
+
 const _ = require("lodash");
 
 set_global("$", global.make_zjquery());
diff --git a/frontend_tests/node_tests/message_flags.js b/frontend_tests/node_tests/message_flags.js
index 8061e09499..aa15926c94 100644
--- a/frontend_tests/node_tests/message_flags.js
+++ b/frontend_tests/node_tests/message_flags.js
@@ -1,3 +1,5 @@
+"use strict";
+
 zrequire("unread");
 zrequire("unread_ops");
 zrequire("message_flags");
diff --git a/frontend_tests/node_tests/message_list.js b/frontend_tests/node_tests/message_list.js
index 6dc9663449..e5f34cf51f 100644
--- a/frontend_tests/node_tests/message_list.js
+++ b/frontend_tests/node_tests/message_list.js
@@ -1,3 +1,5 @@
+"use strict";
+
 // These unit tests for static/js/message_list.js emphasize the model-ish
 // aspects of the MessageList class.  We have to stub out a few functions
 // related to views and events to get the tests working.
diff --git a/frontend_tests/node_tests/message_list_data.js b/frontend_tests/node_tests/message_list_data.js
index 9c5e0335b6..cea13f3fe6 100644
--- a/frontend_tests/node_tests/message_list_data.js
+++ b/frontend_tests/node_tests/message_list_data.js
@@ -1,3 +1,5 @@
+"use strict";
+
 zrequire("unread");
 
 zrequire("Filter", "js/filter");
diff --git a/frontend_tests/node_tests/message_list_view.js b/frontend_tests/node_tests/message_list_view.js
index 115778baac..90d96df366 100644
--- a/frontend_tests/node_tests/message_list_view.js
+++ b/frontend_tests/node_tests/message_list_view.js
@@ -1,3 +1,5 @@
+"use strict";
+
 const _ = require("lodash");
 
 set_global("$", global.make_zjquery());
diff --git a/frontend_tests/node_tests/message_store.js b/frontend_tests/node_tests/message_store.js
index c97a107ce6..142f16b255 100644
--- a/frontend_tests/node_tests/message_store.js
+++ b/frontend_tests/node_tests/message_store.js
@@ -1,3 +1,5 @@
+"use strict";
+
 const util = zrequire("util");
 zrequire("pm_conversations");
 zrequire("people");
diff --git a/frontend_tests/node_tests/muting.js b/frontend_tests/node_tests/muting.js
index 818fa595af..0a0b0ace35 100644
--- a/frontend_tests/node_tests/muting.js
+++ b/frontend_tests/node_tests/muting.js
@@ -1,3 +1,5 @@
+"use strict";
+
 zrequire("timerender");
 zrequire("muting");
 zrequire("stream_data");
diff --git a/frontend_tests/node_tests/narrow.js b/frontend_tests/node_tests/narrow.js
index ac79e42cd3..6e954e0ad9 100644
--- a/frontend_tests/node_tests/narrow.js
+++ b/frontend_tests/node_tests/narrow.js
@@ -1,3 +1,5 @@
+"use strict";
+
 set_global("$", global.make_zjquery());
 zrequire("hash_util");
 zrequire("hashchange");
diff --git a/frontend_tests/node_tests/narrow_activate.js b/frontend_tests/node_tests/narrow_activate.js
index dc3c52abf9..c958e5434d 100644
--- a/frontend_tests/node_tests/narrow_activate.js
+++ b/frontend_tests/node_tests/narrow_activate.js
@@ -1,3 +1,5 @@
+"use strict";
+
 const util = zrequire("util");
 set_global("$", global.make_zjquery());
 
diff --git a/frontend_tests/node_tests/narrow_local.js b/frontend_tests/node_tests/narrow_local.js
index 8bdefccc81..8194b84354 100644
--- a/frontend_tests/node_tests/narrow_local.js
+++ b/frontend_tests/node_tests/narrow_local.js
@@ -1,3 +1,5 @@
+"use strict";
+
 zrequire("Filter", "js/filter");
 zrequire("FetchStatus", "js/fetch_status");
 zrequire("MessageListData", "js/message_list_data");
diff --git a/frontend_tests/node_tests/narrow_state.js b/frontend_tests/node_tests/narrow_state.js
index a8b0adcf6d..79bea63043 100644
--- a/frontend_tests/node_tests/narrow_state.js
+++ b/frontend_tests/node_tests/narrow_state.js
@@ -1,3 +1,5 @@
+"use strict";
+
 zrequire("people");
 zrequire("Filter", "js/filter");
 zrequire("stream_data");
diff --git a/frontend_tests/node_tests/narrow_unread.js b/frontend_tests/node_tests/narrow_unread.js
index e82f20bd06..6f2a7db981 100644
--- a/frontend_tests/node_tests/narrow_unread.js
+++ b/frontend_tests/node_tests/narrow_unread.js
@@ -1,3 +1,5 @@
+"use strict";
+
 zrequire("Filter", "js/filter");
 zrequire("people");
 zrequire("stream_data");
diff --git a/frontend_tests/node_tests/notifications.js b/frontend_tests/node_tests/notifications.js
index a8da203c1f..70354bebab 100644
--- a/frontend_tests/node_tests/notifications.js
+++ b/frontend_tests/node_tests/notifications.js
@@ -1,3 +1,5 @@
+"use strict";
+
 // Dependencies
 set_global(
     "$",
diff --git a/frontend_tests/node_tests/password.js b/frontend_tests/node_tests/password.js
index 8c5449ce45..88fdb5050f 100644
--- a/frontend_tests/node_tests/password.js
+++ b/frontend_tests/node_tests/password.js
@@ -1,3 +1,5 @@
+"use strict";
+
 set_global("zxcvbn", zrequire("zxcvbn", "zxcvbn"));
 zrequire("common");
 
diff --git a/frontend_tests/node_tests/people.js b/frontend_tests/node_tests/people.js
index eac1fe0087..f9c4ba8a66 100644
--- a/frontend_tests/node_tests/people.js
+++ b/frontend_tests/node_tests/people.js
@@ -1,3 +1,5 @@
+"use strict";
+
 const _ = require("lodash");
 const moment = require("moment-timezone");
 const rewiremock = require("rewiremock/node");
diff --git a/frontend_tests/node_tests/people_errors.js b/frontend_tests/node_tests/people_errors.js
index f66f2ce0c3..1c2b1f27d7 100644
--- a/frontend_tests/node_tests/people_errors.js
+++ b/frontend_tests/node_tests/people_errors.js
@@ -1,3 +1,5 @@
+"use strict";
+
 zrequire("people");
 
 const return_false = function () {
diff --git a/frontend_tests/node_tests/pm_conversations.js b/frontend_tests/node_tests/pm_conversations.js
index 02546dc944..fd09bbec6d 100644
--- a/frontend_tests/node_tests/pm_conversations.js
+++ b/frontend_tests/node_tests/pm_conversations.js
@@ -1,3 +1,5 @@
+"use strict";
+
 const pmc = zrequire("pm_conversations");
 
 run_test("partners", () => {
diff --git a/frontend_tests/node_tests/pm_list.js b/frontend_tests/node_tests/pm_list.js
index deb24d5789..a20a22d6aa 100644
--- a/frontend_tests/node_tests/pm_list.js
+++ b/frontend_tests/node_tests/pm_list.js
@@ -1,3 +1,5 @@
+"use strict";
+
 set_global("$", global.make_zjquery());
 
 set_global("narrow_state", {});
diff --git a/frontend_tests/node_tests/poll_widget.js b/frontend_tests/node_tests/poll_widget.js
index eab3eb4ff3..e46631e94e 100644
--- a/frontend_tests/node_tests/poll_widget.js
+++ b/frontend_tests/node_tests/poll_widget.js
@@ -1,3 +1,5 @@
+"use strict";
+
 zrequire("poll_widget");
 
 set_global("$", global.make_zjquery());
diff --git a/frontend_tests/node_tests/popovers.js b/frontend_tests/node_tests/popovers.js
index d2801cb19c..5d8090ecc7 100644
--- a/frontend_tests/node_tests/popovers.js
+++ b/frontend_tests/node_tests/popovers.js
@@ -1,3 +1,5 @@
+"use strict";
+
 const rewiremock = require("rewiremock/node");
 
 set_global("$", global.make_zjquery());
diff --git a/frontend_tests/node_tests/presence.js b/frontend_tests/node_tests/presence.js
index f43d34cd01..cf1007ffa7 100644
--- a/frontend_tests/node_tests/presence.js
+++ b/frontend_tests/node_tests/presence.js
@@ -1,3 +1,5 @@
+"use strict";
+
 const XDate = require("xdate");
 
 zrequire("people");
diff --git a/frontend_tests/node_tests/reactions.js b/frontend_tests/node_tests/reactions.js
index b501887bbb..ee2e276f34 100644
--- a/frontend_tests/node_tests/reactions.js
+++ b/frontend_tests/node_tests/reactions.js
@@ -1,3 +1,5 @@
+"use strict";
+
 set_global("document", "document-stub");
 set_global("$", global.make_zjquery());
 
diff --git a/frontend_tests/node_tests/recent_senders.js b/frontend_tests/node_tests/recent_senders.js
index dd6933689d..f8d6498751 100644
--- a/frontend_tests/node_tests/recent_senders.js
+++ b/frontend_tests/node_tests/recent_senders.js
@@ -1,3 +1,5 @@
+"use strict";
+
 const rs = zrequire("recent_senders");
 
 let next_id = 0;
diff --git a/frontend_tests/node_tests/recent_topics.js b/frontend_tests/node_tests/recent_topics.js
index b4226b6688..a45fe2b9bd 100644
--- a/frontend_tests/node_tests/recent_topics.js
+++ b/frontend_tests/node_tests/recent_topics.js
@@ -1,3 +1,5 @@
+"use strict";
+
 zrequire("message_util");
 
 const noop = () => {};
diff --git a/frontend_tests/node_tests/rendered_markdown.js b/frontend_tests/node_tests/rendered_markdown.js
index db62c1cd0f..84ffa09fb5 100644
--- a/frontend_tests/node_tests/rendered_markdown.js
+++ b/frontend_tests/node_tests/rendered_markdown.js
@@ -1,3 +1,5 @@
+"use strict";
+
 const rm = zrequire("rendered_markdown");
 zrequire("people");
 zrequire("user_groups");
diff --git a/frontend_tests/node_tests/rtl.js b/frontend_tests/node_tests/rtl.js
index 74e6e061cc..71f5609cc5 100644
--- a/frontend_tests/node_tests/rtl.js
+++ b/frontend_tests/node_tests/rtl.js
@@ -1,3 +1,5 @@
+"use strict";
+
 const rtl = zrequire("rtl");
 
 run_test("get_direction", () => {
diff --git a/frontend_tests/node_tests/schema.js b/frontend_tests/node_tests/schema.js
index 98c803110a..2d620047c3 100644
--- a/frontend_tests/node_tests/schema.js
+++ b/frontend_tests/node_tests/schema.js
@@ -1,3 +1,5 @@
+"use strict";
+
 zrequire("schema");
 
 run_test("basics", () => {
diff --git a/frontend_tests/node_tests/scroll_util.js b/frontend_tests/node_tests/scroll_util.js
index 1e3ad161e6..e6bd93b4a7 100644
--- a/frontend_tests/node_tests/scroll_util.js
+++ b/frontend_tests/node_tests/scroll_util.js
@@ -1,3 +1,5 @@
+"use strict";
+
 zrequire("scroll_util");
 set_global("ui", {
     get_scroll_element: (element) => element,
diff --git a/frontend_tests/node_tests/search.js b/frontend_tests/node_tests/search.js
index 319ab38e12..d346e00b41 100644
--- a/frontend_tests/node_tests/search.js
+++ b/frontend_tests/node_tests/search.js
@@ -1,3 +1,5 @@
+"use strict";
+
 set_global("page_params", {
     search_pills_enabled: true,
 });
diff --git a/frontend_tests/node_tests/search_legacy.js b/frontend_tests/node_tests/search_legacy.js
index edf77f4d41..7efaccf4b5 100644
--- a/frontend_tests/node_tests/search_legacy.js
+++ b/frontend_tests/node_tests/search_legacy.js
@@ -1,3 +1,5 @@
+"use strict";
+
 set_global("page_params", {
     search_pills_enabled: false,
 });
diff --git a/frontend_tests/node_tests/search_pill.js b/frontend_tests/node_tests/search_pill.js
index b26776af02..c588f3e4ab 100644
--- a/frontend_tests/node_tests/search_pill.js
+++ b/frontend_tests/node_tests/search_pill.js
@@ -1,3 +1,5 @@
+"use strict";
+
 zrequire("search_pill");
 zrequire("input_pill");
 zrequire("Filter", "js/filter");
diff --git a/frontend_tests/node_tests/search_suggestion.js b/frontend_tests/node_tests/search_suggestion.js
index 5bb1cbd590..fbe017e1a4 100644
--- a/frontend_tests/node_tests/search_suggestion.js
+++ b/frontend_tests/node_tests/search_suggestion.js
@@ -1,3 +1,5 @@
+"use strict";
+
 set_global("page_params", {
     search_pills_enabled: true,
 });
diff --git a/frontend_tests/node_tests/search_suggestion_legacy.js b/frontend_tests/node_tests/search_suggestion_legacy.js
index 301502879b..443badd619 100644
--- a/frontend_tests/node_tests/search_suggestion_legacy.js
+++ b/frontend_tests/node_tests/search_suggestion_legacy.js
@@ -1,3 +1,5 @@
+"use strict";
+
 set_global("page_params", {
     search_pills_enabled: false,
 });
diff --git a/frontend_tests/node_tests/server_events.js b/frontend_tests/node_tests/server_events.js
index fc2bb7ec7a..31cb1a6019 100644
--- a/frontend_tests/node_tests/server_events.js
+++ b/frontend_tests/node_tests/server_events.js
@@ -1,3 +1,5 @@
+"use strict";
+
 const noop = function () {};
 
 set_global("document", {});
diff --git a/frontend_tests/node_tests/settings_bots.js b/frontend_tests/node_tests/settings_bots.js
index 275b8de5fd..196dcf1143 100644
--- a/frontend_tests/node_tests/settings_bots.js
+++ b/frontend_tests/node_tests/settings_bots.js
@@ -1,3 +1,5 @@
+"use strict";
+
 const rewiremock = require("rewiremock/node");
 
 set_global("page_params", {
diff --git a/frontend_tests/node_tests/settings_data.js b/frontend_tests/node_tests/settings_data.js
index bf04298ee2..9261e11424 100644
--- a/frontend_tests/node_tests/settings_data.js
+++ b/frontend_tests/node_tests/settings_data.js
@@ -1,3 +1,5 @@
+"use strict";
+
 const settings_data = zrequire("settings_data");
 const settings_config = zrequire("settings_config");
 
diff --git a/frontend_tests/node_tests/settings_emoji.js b/frontend_tests/node_tests/settings_emoji.js
index d72a88b4e7..743a4f7848 100644
--- a/frontend_tests/node_tests/settings_emoji.js
+++ b/frontend_tests/node_tests/settings_emoji.js
@@ -1,3 +1,5 @@
+"use strict";
+
 set_global("$", global.make_zjquery());
 set_global("upload_widget", {});
 zrequire("settings_emoji");
diff --git a/frontend_tests/node_tests/settings_muting.js b/frontend_tests/node_tests/settings_muting.js
index c0a980dd6b..869821e7c0 100644
--- a/frontend_tests/node_tests/settings_muting.js
+++ b/frontend_tests/node_tests/settings_muting.js
@@ -1,3 +1,5 @@
+"use strict";
+
 set_global("$", global.make_zjquery());
 set_global("XDate", zrequire("XDate", "xdate"));
 
diff --git a/frontend_tests/node_tests/settings_org.js b/frontend_tests/node_tests/settings_org.js
index 5d4a45215a..6499bfe171 100644
--- a/frontend_tests/node_tests/settings_org.js
+++ b/frontend_tests/node_tests/settings_org.js
@@ -1,3 +1,5 @@
+"use strict";
+
 set_global("$", global.make_zjquery());
 
 const noop = () => {};
diff --git a/frontend_tests/node_tests/settings_profile_fields.js b/frontend_tests/node_tests/settings_profile_fields.js
index 7f39d6fd6c..e818ca9419 100644
--- a/frontend_tests/node_tests/settings_profile_fields.js
+++ b/frontend_tests/node_tests/settings_profile_fields.js
@@ -1,3 +1,5 @@
+"use strict";
+
 const rewiremock = require("rewiremock/node");
 
 set_global("page_params", {});
diff --git a/frontend_tests/node_tests/settings_user_groups.js b/frontend_tests/node_tests/settings_user_groups.js
index 4f9953c336..36747501c9 100644
--- a/frontend_tests/node_tests/settings_user_groups.js
+++ b/frontend_tests/node_tests/settings_user_groups.js
@@ -1,3 +1,5 @@
+"use strict";
+
 const _ = require("lodash");
 
 zrequire("user_pill");
diff --git a/frontend_tests/node_tests/spoilers.js b/frontend_tests/node_tests/spoilers.js
index d3a8d76bb4..81b48f6ebd 100644
--- a/frontend_tests/node_tests/spoilers.js
+++ b/frontend_tests/node_tests/spoilers.js
@@ -1,3 +1,5 @@
+"use strict";
+
 set_global("$", global.make_zjquery());
 zrequire("spoilers");
 
diff --git a/frontend_tests/node_tests/stream_data.js b/frontend_tests/node_tests/stream_data.js
index 990a467da7..a3ac443bf8 100644
--- a/frontend_tests/node_tests/stream_data.js
+++ b/frontend_tests/node_tests/stream_data.js
@@ -1,3 +1,5 @@
+"use strict";
+
 const _ = require("lodash");
 
 set_global("page_params", {
diff --git a/frontend_tests/node_tests/stream_events.js b/frontend_tests/node_tests/stream_events.js
index 9ce2f76e35..2198b20475 100644
--- a/frontend_tests/node_tests/stream_events.js
+++ b/frontend_tests/node_tests/stream_events.js
@@ -1,3 +1,5 @@
+"use strict";
+
 const noop = function () {};
 const return_true = function () {
     return true;
diff --git a/frontend_tests/node_tests/stream_list.js b/frontend_tests/node_tests/stream_list.js
index 0b486be7e8..92382e0470 100644
--- a/frontend_tests/node_tests/stream_list.js
+++ b/frontend_tests/node_tests/stream_list.js
@@ -1,3 +1,5 @@
+"use strict";
+
 set_global("document", "document-stub");
 set_global("$", global.make_zjquery());
 
diff --git a/frontend_tests/node_tests/stream_search.js b/frontend_tests/node_tests/stream_search.js
index a5329b8760..fbe49d960a 100644
--- a/frontend_tests/node_tests/stream_search.js
+++ b/frontend_tests/node_tests/stream_search.js
@@ -1,3 +1,5 @@
+"use strict";
+
 // This tests the stream searching functionality which currently
 // lives in stream_list.js.
 
diff --git a/frontend_tests/node_tests/stream_sort.js b/frontend_tests/node_tests/stream_sort.js
index a766e2a5fa..bba41a1a22 100644
--- a/frontend_tests/node_tests/stream_sort.js
+++ b/frontend_tests/node_tests/stream_sort.js
@@ -1,3 +1,5 @@
+"use strict";
+
 zrequire("stream_data");
 zrequire("stream_sort");
 
diff --git a/frontend_tests/node_tests/stream_topic_history.js b/frontend_tests/node_tests/stream_topic_history.js
index a5850fd870..03bf10fa6e 100644
--- a/frontend_tests/node_tests/stream_topic_history.js
+++ b/frontend_tests/node_tests/stream_topic_history.js
@@ -1,3 +1,5 @@
+"use strict";
+
 zrequire("unread");
 zrequire("stream_data");
 zrequire("stream_topic_history");
diff --git a/frontend_tests/node_tests/submessage.js b/frontend_tests/node_tests/submessage.js
index 915605b992..fa26f88eb7 100644
--- a/frontend_tests/node_tests/submessage.js
+++ b/frontend_tests/node_tests/submessage.js
@@ -1,3 +1,5 @@
+"use strict";
+
 zrequire("submessage");
 
 set_global("channel", {});
diff --git a/frontend_tests/node_tests/subs.js b/frontend_tests/node_tests/subs.js
index d92e46c769..6ecaab424f 100644
--- a/frontend_tests/node_tests/subs.js
+++ b/frontend_tests/node_tests/subs.js
@@ -1,3 +1,5 @@
+"use strict";
+
 global.stub_out_jquery();
 
 set_global("ui", {
diff --git a/frontend_tests/node_tests/support.js b/frontend_tests/node_tests/support.js
index 298a2cd35a..da8fe89800 100644
--- a/frontend_tests/node_tests/support.js
+++ b/frontend_tests/node_tests/support.js
@@ -1,3 +1,5 @@
+"use strict";
+
 const fs = require("fs");
 
 const {JSDOM} = require("jsdom");
diff --git a/frontend_tests/node_tests/timerender.js b/frontend_tests/node_tests/timerender.js
index 99933f53a9..1762a023ff 100644
--- a/frontend_tests/node_tests/timerender.js
+++ b/frontend_tests/node_tests/timerender.js
@@ -1,3 +1,5 @@
+"use strict";
+
 const moment = require("moment");
 const XDate = require("xdate");
 
diff --git a/frontend_tests/node_tests/top_left_corner.js b/frontend_tests/node_tests/top_left_corner.js
index dfcbd815e3..c4cfb14f23 100644
--- a/frontend_tests/node_tests/top_left_corner.js
+++ b/frontend_tests/node_tests/top_left_corner.js
@@ -1,3 +1,5 @@
+"use strict";
+
 set_global("$", global.make_zjquery());
 
 zrequire("Filter", "js/filter");
diff --git a/frontend_tests/node_tests/topic_generator.js b/frontend_tests/node_tests/topic_generator.js
index 4342e42107..b944533a61 100644
--- a/frontend_tests/node_tests/topic_generator.js
+++ b/frontend_tests/node_tests/topic_generator.js
@@ -1,3 +1,5 @@
+"use strict";
+
 set_global("pm_conversations", {
     recent: {},
 });
diff --git a/frontend_tests/node_tests/topic_list_data.js b/frontend_tests/node_tests/topic_list_data.js
index 3595654e4f..d3f3ad1060 100644
--- a/frontend_tests/node_tests/topic_list_data.js
+++ b/frontend_tests/node_tests/topic_list_data.js
@@ -1,3 +1,5 @@
+"use strict";
+
 const _ = require("lodash");
 
 set_global("narrow_state", {});
diff --git a/frontend_tests/node_tests/transmit.js b/frontend_tests/node_tests/transmit.js
index a7381f1799..b300a50a8d 100644
--- a/frontend_tests/node_tests/transmit.js
+++ b/frontend_tests/node_tests/transmit.js
@@ -1,3 +1,5 @@
+"use strict";
+
 const noop = function () {};
 
 set_global("$", global.make_zjquery());
diff --git a/frontend_tests/node_tests/typeahead.js b/frontend_tests/node_tests/typeahead.js
index 301a44c0bc..0220603b2e 100644
--- a/frontend_tests/node_tests/typeahead.js
+++ b/frontend_tests/node_tests/typeahead.js
@@ -1,3 +1,5 @@
+"use strict";
+
 const typeahead = zrequire("typeahead", "shared/js/typeahead");
 
 // The data structures here may be different for
diff --git a/frontend_tests/node_tests/typeahead_helper.js b/frontend_tests/node_tests/typeahead_helper.js
index a1911f766c..5627e475f4 100644
--- a/frontend_tests/node_tests/typeahead_helper.js
+++ b/frontend_tests/node_tests/typeahead_helper.js
@@ -1,3 +1,5 @@
+"use strict";
+
 set_global("page_params", {realm_is_zephyr_mirror_realm: false});
 set_global("md5", (s) => "md5-" + s);
 
diff --git a/frontend_tests/node_tests/typing_data.js b/frontend_tests/node_tests/typing_data.js
index 7b5f09f891..d1f2b8a768 100644
--- a/frontend_tests/node_tests/typing_data.js
+++ b/frontend_tests/node_tests/typing_data.js
@@ -1,3 +1,5 @@
+"use strict";
+
 zrequire("typing_data");
 
 run_test("basics", () => {
diff --git a/frontend_tests/node_tests/typing_status.js b/frontend_tests/node_tests/typing_status.js
index f3ebf0c54e..ffcda32a55 100644
--- a/frontend_tests/node_tests/typing_status.js
+++ b/frontend_tests/node_tests/typing_status.js
@@ -1,3 +1,5 @@
+"use strict";
+
 zrequire("typing");
 zrequire("people");
 zrequire("compose_pm_pill");
diff --git a/frontend_tests/node_tests/ui.js b/frontend_tests/node_tests/ui.js
index b7357d3e82..8ed2e3eb26 100644
--- a/frontend_tests/node_tests/ui.js
+++ b/frontend_tests/node_tests/ui.js
@@ -1,3 +1,5 @@
+"use strict";
+
 const ui = zrequire("ui");
 
 set_global("navigator", {
diff --git a/frontend_tests/node_tests/ui_init.js b/frontend_tests/node_tests/ui_init.js
index 514f3a34e7..c5779f652f 100644
--- a/frontend_tests/node_tests/ui_init.js
+++ b/frontend_tests/node_tests/ui_init.js
@@ -1,3 +1,5 @@
+"use strict";
+
 const rewiremock = require("rewiremock/node");
 
 /*
diff --git a/frontend_tests/node_tests/unread.js b/frontend_tests/node_tests/unread.js
index 41648abdb1..3daf58a8b4 100644
--- a/frontend_tests/node_tests/unread.js
+++ b/frontend_tests/node_tests/unread.js
@@ -1,3 +1,5 @@
+"use strict";
+
 const _ = require("lodash");
 
 zrequire("muting");
diff --git a/frontend_tests/node_tests/upgrade.js b/frontend_tests/node_tests/upgrade.js
index 9b8a8bc904..67fc85c20c 100644
--- a/frontend_tests/node_tests/upgrade.js
+++ b/frontend_tests/node_tests/upgrade.js
@@ -1,3 +1,5 @@
+"use strict";
+
 const noop = () => {};
 const fs = require("fs");
 
diff --git a/frontend_tests/node_tests/upload.js b/frontend_tests/node_tests/upload.js
index 856eaa1cb0..fd2757a832 100644
--- a/frontend_tests/node_tests/upload.js
+++ b/frontend_tests/node_tests/upload.js
@@ -1,3 +1,5 @@
+"use strict";
+
 const rewiremock = require("rewiremock/node");
 
 set_global("$", global.make_zjquery());
diff --git a/frontend_tests/node_tests/user_events.js b/frontend_tests/node_tests/user_events.js
index f74dc5910c..a4a17ace61 100644
--- a/frontend_tests/node_tests/user_events.js
+++ b/frontend_tests/node_tests/user_events.js
@@ -1,3 +1,5 @@
+"use strict";
+
 set_global("$", global.make_zjquery());
 
 zrequire("people");
diff --git a/frontend_tests/node_tests/user_groups.js b/frontend_tests/node_tests/user_groups.js
index 78eb697135..3a7a47dbd4 100644
--- a/frontend_tests/node_tests/user_groups.js
+++ b/frontend_tests/node_tests/user_groups.js
@@ -1,3 +1,5 @@
+"use strict";
+
 zrequire("user_groups");
 
 run_test("user_groups", () => {
diff --git a/frontend_tests/node_tests/user_pill.js b/frontend_tests/node_tests/user_pill.js
index da9492aefe..6abd113b9c 100644
--- a/frontend_tests/node_tests/user_pill.js
+++ b/frontend_tests/node_tests/user_pill.js
@@ -1,3 +1,5 @@
+"use strict";
+
 zrequire("people");
 set_global("md5", (s) => "md5-" + s);
 zrequire("user_pill");
diff --git a/frontend_tests/node_tests/user_status.js b/frontend_tests/node_tests/user_status.js
index 4295223b48..434d99b205 100644
--- a/frontend_tests/node_tests/user_status.js
+++ b/frontend_tests/node_tests/user_status.js
@@ -1,3 +1,5 @@
+"use strict";
+
 set_global("channel", {});
 zrequire("user_status");
 
diff --git a/frontend_tests/node_tests/util.js b/frontend_tests/node_tests/util.js
index 50e4778720..5f8bfd10d5 100644
--- a/frontend_tests/node_tests/util.js
+++ b/frontend_tests/node_tests/util.js
@@ -1,3 +1,5 @@
+"use strict";
+
 const {JSDOM} = require("jsdom");
 const _ = require("lodash");
 
diff --git a/frontend_tests/node_tests/vdom.js b/frontend_tests/node_tests/vdom.js
index 6ccb22e7c8..4f84a83d2d 100644
--- a/frontend_tests/node_tests/vdom.js
+++ b/frontend_tests/node_tests/vdom.js
@@ -1,3 +1,5 @@
+"use strict";
+
 zrequire("vdom");
 
 run_test("basics", () => {
diff --git a/frontend_tests/node_tests/widgetize.js b/frontend_tests/node_tests/widgetize.js
index 275689ec57..269dbd0add 100644
--- a/frontend_tests/node_tests/widgetize.js
+++ b/frontend_tests/node_tests/widgetize.js
@@ -1,3 +1,5 @@
+"use strict";
+
 set_global("$", global.make_zjquery());
 set_global("poll_widget", {});
 set_global("tictactoe_widget", {});
diff --git a/frontend_tests/node_tests/zblueslip.js b/frontend_tests/node_tests/zblueslip.js
index 52214d1fd1..10373f8839 100644
--- a/frontend_tests/node_tests/zblueslip.js
+++ b/frontend_tests/node_tests/zblueslip.js
@@ -1,3 +1,5 @@
+"use strict";
+
 /*
 
 This test module actually tests our test code, particularly zblueslip, and
diff --git a/frontend_tests/node_tests/zjquery.js b/frontend_tests/node_tests/zjquery.js
index 4fe716e89b..33123a8970 100644
--- a/frontend_tests/node_tests/zjquery.js
+++ b/frontend_tests/node_tests/zjquery.js
@@ -1,3 +1,5 @@
+"use strict";
+
 /*
 
 This test module actually tests our test code, particularly zjquery, and
diff --git a/frontend_tests/puppeteer_lib/common.js b/frontend_tests/puppeteer_lib/common.js
index 81ecd15042..d3d0b014f7 100644
--- a/frontend_tests/puppeteer_lib/common.js
+++ b/frontend_tests/puppeteer_lib/common.js
@@ -1,3 +1,5 @@
+"use strict";
+
 const assert = require("assert").strict;
 const path = require("path");
 
diff --git a/frontend_tests/puppeteer_tests/00-realm-creation.js b/frontend_tests/puppeteer_tests/00-realm-creation.js
index 979257b5fb..666d9d3f30 100644
--- a/frontend_tests/puppeteer_tests/00-realm-creation.js
+++ b/frontend_tests/puppeteer_tests/00-realm-creation.js
@@ -1,3 +1,5 @@
+"use strict";
+
 const assert = require("assert").strict;
 
 const common = require("../puppeteer_lib/common");
diff --git a/frontend_tests/puppeteer_tests/01-login.js b/frontend_tests/puppeteer_tests/01-login.js
index c584018bfb..9c76b4094f 100644
--- a/frontend_tests/puppeteer_tests/01-login.js
+++ b/frontend_tests/puppeteer_tests/01-login.js
@@ -1,3 +1,5 @@
+"use strict";
+
 const test_credentials = require("../../var/casper/test_credentials.js").test_credentials;
 const common = require("../puppeteer_lib/common");
 
diff --git a/frontend_tests/puppeteer_tests/02-message-basics.js b/frontend_tests/puppeteer_tests/02-message-basics.js
index baa49ad96e..e85ac8dc5f 100644
--- a/frontend_tests/puppeteer_tests/02-message-basics.js
+++ b/frontend_tests/puppeteer_tests/02-message-basics.js
@@ -1,3 +1,5 @@
+"use strict";
+
 const common = require("../puppeteer_lib/common");
 
 async function message_basic_tests(page) {
diff --git a/frontend_tests/puppeteer_tests/03-compose.js b/frontend_tests/puppeteer_tests/03-compose.js
index 2f482aeb74..8a398c763b 100644
--- a/frontend_tests/puppeteer_tests/03-compose.js
+++ b/frontend_tests/puppeteer_tests/03-compose.js
@@ -1,3 +1,5 @@
+"use strict";
+
 const assert = require("assert").strict;
 
 const common = require("../puppeteer_lib/common");
diff --git a/frontend_tests/puppeteer_tests/04-subscriptions.js b/frontend_tests/puppeteer_tests/04-subscriptions.js
index e3d4ca9496..86f68db952 100644
--- a/frontend_tests/puppeteer_tests/04-subscriptions.js
+++ b/frontend_tests/puppeteer_tests/04-subscriptions.js
@@ -1,3 +1,5 @@
+"use strict";
+
 const assert = require("assert").strict;
 
 const common = require("../puppeteer_lib/common");
diff --git a/frontend_tests/puppeteer_tests/05-settings.js b/frontend_tests/puppeteer_tests/05-settings.js
index ecc44518ad..8809599249 100644
--- a/frontend_tests/puppeteer_tests/05-settings.js
+++ b/frontend_tests/puppeteer_tests/05-settings.js
@@ -1,3 +1,5 @@
+"use strict";
+
 const assert = require("assert").strict;
 
 const test_credentials = require("../../var/casper/test_credentials.js").test_credentials;
diff --git a/frontend_tests/zjsunit/finder.js b/frontend_tests/zjsunit/finder.js
index e5adbacfb4..c1eadba325 100644
--- a/frontend_tests/zjsunit/finder.js
+++ b/frontend_tests/zjsunit/finder.js
@@ -1,3 +1,5 @@
+"use strict";
+
 const fs = require("fs");
 const path = require("path");
 
diff --git a/frontend_tests/zjsunit/handlebars.js b/frontend_tests/zjsunit/handlebars.js
index 9daafc87e2..71aa47f189 100644
--- a/frontend_tests/zjsunit/handlebars.js
+++ b/frontend_tests/zjsunit/handlebars.js
@@ -1,3 +1,5 @@
+"use strict";
+
 const fs = require("fs");
 const path = require("path");
 
diff --git a/frontend_tests/zjsunit/i18n.js b/frontend_tests/zjsunit/i18n.js
index 956a559efa..b9e96958bd 100644
--- a/frontend_tests/zjsunit/i18n.js
+++ b/frontend_tests/zjsunit/i18n.js
@@ -1,3 +1,5 @@
+"use strict";
+
 exports.t = function (str, context) {
     // HAPPY PATH: most translations are a simple string:
     if (context === undefined) {
diff --git a/frontend_tests/zjsunit/index.js b/frontend_tests/zjsunit/index.js
index f31afc9c3d..ecab7ef6b4 100644
--- a/frontend_tests/zjsunit/index.js
+++ b/frontend_tests/zjsunit/index.js
@@ -1,3 +1,5 @@
+"use strict";
+
 const fs = require("fs");
 const Module = require("module");
 const path = require("path");
diff --git a/frontend_tests/zjsunit/markdown_assert.js b/frontend_tests/zjsunit/markdown_assert.js
index 73778525fb..e6f6e7648e 100644
--- a/frontend_tests/zjsunit/markdown_assert.js
+++ b/frontend_tests/zjsunit/markdown_assert.js
@@ -1,3 +1,5 @@
+"use strict";
+
 /**
  * markdown_assert.js
  *
diff --git a/frontend_tests/zjsunit/mdiff.js b/frontend_tests/zjsunit/mdiff.js
index 36b8ed0c44..d312769b6e 100644
--- a/frontend_tests/zjsunit/mdiff.js
+++ b/frontend_tests/zjsunit/mdiff.js
@@ -1,3 +1,5 @@
+"use strict";
+
 /**
  * mdiff.js
  *
diff --git a/frontend_tests/zjsunit/namespace.js b/frontend_tests/zjsunit/namespace.js
index effe06e6c3..119cc6d2b7 100644
--- a/frontend_tests/zjsunit/namespace.js
+++ b/frontend_tests/zjsunit/namespace.js
@@ -1,3 +1,5 @@
+"use strict";
+
 const _ = require("lodash");
 
 const requires = [];
diff --git a/frontend_tests/zjsunit/stub.js b/frontend_tests/zjsunit/stub.js
index 81a7e19d00..b39e1db720 100644
--- a/frontend_tests/zjsunit/stub.js
+++ b/frontend_tests/zjsunit/stub.js
@@ -1,3 +1,5 @@
+"use strict";
+
 const assert = require("assert").strict;
 
 // Stubs don't do any magical modifications to your namespace.  They
diff --git a/frontend_tests/zjsunit/zblueslip.js b/frontend_tests/zjsunit/zblueslip.js
index b7f8fa9dab..ea74ade7e2 100644
--- a/frontend_tests/zjsunit/zblueslip.js
+++ b/frontend_tests/zjsunit/zblueslip.js
@@ -1,3 +1,5 @@
+"use strict";
+
 exports.make_zblueslip = function () {
     const lib = {};
 
diff --git a/frontend_tests/zjsunit/zjquery.js b/frontend_tests/zjsunit/zjquery.js
index fc96b00f30..a1fe1fc076 100644
--- a/frontend_tests/zjsunit/zjquery.js
+++ b/frontend_tests/zjsunit/zjquery.js
@@ -1,3 +1,5 @@
+"use strict";
+
 const noop = function () {};
 
 class Event {
diff --git a/postcss.config.js b/postcss.config.js
index 35f9b9b0f9..10620d2ab8 100644
--- a/postcss.config.js
+++ b/postcss.config.js
@@ -1,3 +1,5 @@
+"use strict";
+
 module.exports = ({file}) => ({
     parser: file.extname === ".scss" ? "postcss-scss" : false,
     plugins: {
diff --git a/prettier.config.js b/prettier.config.js
index c638745810..1966c858a3 100644
--- a/prettier.config.js
+++ b/prettier.config.js
@@ -1,3 +1,5 @@
+"use strict";
+
 module.exports = {
     bracketSpacing: false,
     trailingComma: "all",
diff --git a/static/assets/icons/zulip-icons.font.js b/static/assets/icons/zulip-icons.font.js
index 3136e6c8ef..5ef0b11a74 100644
--- a/static/assets/icons/zulip-icons.font.js
+++ b/static/assets/icons/zulip-icons.font.js
@@ -1,3 +1,5 @@
+"use strict";
+
 module.exports = {
     files: ["./*.svg"],
     fontName: "zulip-icons",
diff --git a/static/js/activity.js b/static/js/activity.js
index fe65dc5de7..8da6994193 100644
--- a/static/js/activity.js
+++ b/static/js/activity.js
@@ -1,3 +1,5 @@
+"use strict";
+
 const _ = require("lodash");
 /*
     Helpers for detecting user activity and managing user idle states
diff --git a/static/js/admin.js b/static/js/admin.js
index e5772411e2..0c8508ba67 100644
--- a/static/js/admin.js
+++ b/static/js/admin.js
@@ -1,3 +1,5 @@
+"use strict";
+
 const render_admin_tab = require("../templates/admin_tab.hbs");
 const render_settings_organization_settings_tip = require("../templates/settings/organization_settings_tip.hbs");
 
diff --git a/static/js/alert_words.js b/static/js/alert_words.js
index 8968d2fbce..96861f1119 100644
--- a/static/js/alert_words.js
+++ b/static/js/alert_words.js
@@ -1,3 +1,5 @@
+"use strict";
+
 const _ = require("lodash");
 
 // For simplicity, we use a list for our internal
diff --git a/static/js/alert_words_ui.js b/static/js/alert_words_ui.js
index 2a86a3e41f..a132ed5ba2 100644
--- a/static/js/alert_words_ui.js
+++ b/static/js/alert_words_ui.js
@@ -1,3 +1,5 @@
+"use strict";
+
 const render_alert_word_settings_item = require("../templates/settings/alert_word_settings_item.hbs");
 
 exports.render_alert_words_ui = function () {
diff --git a/static/js/analytics/activity.js b/static/js/analytics/activity.js
index 5a17aff7f1..ea5cbe3e0f 100644
--- a/static/js/analytics/activity.js
+++ b/static/js/analytics/activity.js
@@ -1,3 +1,5 @@
+"use strict";
+
 $(() => {
     $("a.envelope-link").on("click", function () {
         common.copy_data_attribute_value($(this), "admin-emails");
diff --git a/static/js/analytics/support.js b/static/js/analytics/support.js
index 46aba1eda8..fdfb141a0f 100644
--- a/static/js/analytics/support.js
+++ b/static/js/analytics/support.js
@@ -1,3 +1,5 @@
+"use strict";
+
 $(() => {
     $("body").on("click", ".scrub-realm-button", function (e) {
         e.preventDefault();
diff --git a/static/js/archive.js b/static/js/archive.js
index 07b3f40131..993d78885c 100644
--- a/static/js/archive.js
+++ b/static/js/archive.js
@@ -1,3 +1,5 @@
+"use strict";
+
 const _ = require("lodash");
 const XDate = require("xdate");
 
diff --git a/static/js/attachments_ui.js b/static/js/attachments_ui.js
index 6436c62a23..fca9190765 100644
--- a/static/js/attachments_ui.js
+++ b/static/js/attachments_ui.js
@@ -1,3 +1,5 @@
+"use strict";
+
 const XDate = require("xdate");
 
 const render_settings_upload_space_stats = require("../templates/settings/upload_space_stats.hbs");
diff --git a/static/js/avatar.js b/static/js/avatar.js
index 4509431565..cac45998c1 100644
--- a/static/js/avatar.js
+++ b/static/js/avatar.js
@@ -1,3 +1,5 @@
+"use strict";
+
 exports.build_bot_create_widget = function () {
     // We have to do strange gyrations with the file input to clear it,
     // where we replace it wholesale, so we generalize the file input with
diff --git a/static/js/billing/billing.js b/static/js/billing/billing.js
index ca553c30bc..c6b54b059a 100644
--- a/static/js/billing/billing.js
+++ b/static/js/billing/billing.js
@@ -1,3 +1,5 @@
+"use strict";
+
 exports.initialize = function () {
     helpers.set_tab("billing");
 
diff --git a/static/js/billing/helpers.js b/static/js/billing/helpers.js
index 5d3a33d378..0368b0320d 100644
--- a/static/js/billing/helpers.js
+++ b/static/js/billing/helpers.js
@@ -1,3 +1,5 @@
+"use strict";
+
 exports.create_ajax_request = function (
     url,
     form_name,
diff --git a/static/js/billing/upgrade.js b/static/js/billing/upgrade.js
index cb4f7cc4fc..ab0f344f30 100644
--- a/static/js/billing/upgrade.js
+++ b/static/js/billing/upgrade.js
@@ -1,3 +1,5 @@
+"use strict";
+
 exports.initialize = () => {
     helpers.set_tab("upgrade");
 
diff --git a/static/js/blueslip.js b/static/js/blueslip.js
index 094b7e8078..858d7d78c3 100644
--- a/static/js/blueslip.js
+++ b/static/js/blueslip.js
@@ -1,3 +1,5 @@
+"use strict";
+
 /* eslint-disable no-console */
 
 // System documented in https://zulip.readthedocs.io/en/latest/subsystems/logging.html
diff --git a/static/js/bot_data.js b/static/js/bot_data.js
index 3244ac91d8..d8327769ea 100644
--- a/static/js/bot_data.js
+++ b/static/js/bot_data.js
@@ -1,3 +1,5 @@
+"use strict";
+
 const _ = require("lodash");
 
 const bots = new Map();
diff --git a/static/js/buddy_data.js b/static/js/buddy_data.js
index 29920bd59e..59851cad92 100644
--- a/static/js/buddy_data.js
+++ b/static/js/buddy_data.js
@@ -1,3 +1,5 @@
+"use strict";
+
 const util = require("./util");
 /*
 
diff --git a/static/js/buddy_list.js b/static/js/buddy_list.js
index b4d6c67f6b..81eca86a1d 100644
--- a/static/js/buddy_list.js
+++ b/static/js/buddy_list.js
@@ -1,3 +1,5 @@
+"use strict";
+
 const render_user_presence_row = require("../templates/user_presence_row.hbs");
 const render_user_presence_rows = require("../templates/user_presence_rows.hbs");
 
diff --git a/static/js/channel.js b/static/js/channel.js
index 23db2598b0..1cf077b672 100644
--- a/static/js/channel.js
+++ b/static/js/channel.js
@@ -1,3 +1,5 @@
+"use strict";
+
 const pending_requests = [];
 
 function add_pending_request(jqXHR) {
diff --git a/static/js/click_handlers.js b/static/js/click_handlers.js
index 789c30390a..33e1d09d83 100644
--- a/static/js/click_handlers.js
+++ b/static/js/click_handlers.js
@@ -1,3 +1,5 @@
+"use strict";
+
 const _ = require("lodash");
 const WinChan = require("winchan");
 
diff --git a/static/js/color_data.js b/static/js/color_data.js
index 6a9da6d296..e62eff0441 100644
--- a/static/js/color_data.js
+++ b/static/js/color_data.js
@@ -1,3 +1,5 @@
+"use strict";
+
 const _ = require("lodash");
 // These colors are used now for streams.
 const stream_colors = [
diff --git a/static/js/colorspace.js b/static/js/colorspace.js
index 8fb5f1b797..3096f46e62 100644
--- a/static/js/colorspace.js
+++ b/static/js/colorspace.js
@@ -1,3 +1,5 @@
+"use strict";
+
 // Convert an sRGB value in [0, 255] to a linear intensity
 // value in [0, 1].
 //
diff --git a/static/js/common.js b/static/js/common.js
index 65a18c3812..ac36d6d5ab 100644
--- a/static/js/common.js
+++ b/static/js/common.js
@@ -1,3 +1,5 @@
+"use strict";
+
 // This reloads the module in development rather than refreshing the page
 if (module.hot) {
     module.hot.accept();
diff --git a/static/js/components.js b/static/js/components.js
index dd71507660..5a11559e86 100644
--- a/static/js/components.js
+++ b/static/js/components.js
@@ -1,3 +1,5 @@
+"use strict";
+
 /* USAGE:
     Toggle x = components.toggle({
         selected: Integer selected_index,
diff --git a/static/js/compose.js b/static/js/compose.js
index 2f56b71949..c2b76fb132 100644
--- a/static/js/compose.js
+++ b/static/js/compose.js
@@ -1,3 +1,5 @@
+"use strict";
+
 const Handlebars = require("handlebars/runtime");
 
 const render_compose_all_everyone = require("../templates/compose_all_everyone.hbs");
diff --git a/static/js/compose_actions.js b/static/js/compose_actions.js
index 84d41da982..426023cc8c 100644
--- a/static/js/compose_actions.js
+++ b/static/js/compose_actions.js
@@ -1,3 +1,5 @@
+"use strict";
+
 const autosize = require("autosize");
 
 const fenced_code = require("../shared/js/fenced_code");
diff --git a/static/js/compose_fade.js b/static/js/compose_fade.js
index bf1aef1850..d6093e16e5 100644
--- a/static/js/compose_fade.js
+++ b/static/js/compose_fade.js
@@ -1,3 +1,5 @@
+"use strict";
+
 const _ = require("lodash");
 
 const util = require("./util");
diff --git a/static/js/compose_pm_pill.js b/static/js/compose_pm_pill.js
index b9d7a2a598..86b14c5496 100644
--- a/static/js/compose_pm_pill.js
+++ b/static/js/compose_pm_pill.js
@@ -1,3 +1,5 @@
+"use strict";
+
 const util = require("./util");
 
 exports.initialize_pill = function () {
diff --git a/static/js/compose_state.js b/static/js/compose_state.js
index b42eca74a8..38ce7b664e 100644
--- a/static/js/compose_state.js
+++ b/static/js/compose_state.js
@@ -1,3 +1,5 @@
+"use strict";
+
 let message_type = false; // 'stream', 'private', or false-y
 
 exports.set_message_type = function (msg_type) {
diff --git a/static/js/compose_ui.js b/static/js/compose_ui.js
index 3cb876d715..35cd98e152 100644
--- a/static/js/compose_ui.js
+++ b/static/js/compose_ui.js
@@ -1,3 +1,5 @@
+"use strict";
+
 const autosize = require("autosize");
 
 exports.autosize_textarea = function () {
diff --git a/static/js/composebox_typeahead.js b/static/js/composebox_typeahead.js
index df3d197a42..5d008cf8b6 100644
--- a/static/js/composebox_typeahead.js
+++ b/static/js/composebox_typeahead.js
@@ -1,3 +1,5 @@
+"use strict";
+
 const autosize = require("autosize");
 const confirmDatePlugin = require("flatpickr/dist/plugins/confirmDate/confirmDate.js");
 const moment = require("moment");
diff --git a/static/js/condense.js b/static/js/condense.js
index 929213acfe..9dca9f9f39 100644
--- a/static/js/condense.js
+++ b/static/js/condense.js
@@ -1,3 +1,5 @@
+"use strict";
+
 /*
 This library implements two related, similar concepts:
 
diff --git a/static/js/confirm_dialog.js b/static/js/confirm_dialog.js
index b13d54b023..a638b1ac13 100644
--- a/static/js/confirm_dialog.js
+++ b/static/js/confirm_dialog.js
@@ -1,3 +1,5 @@
+"use strict";
+
 const render_confirm_dialog = require("../templates/confirm_dialog.hbs");
 
 /*
diff --git a/static/js/copy_and_paste.js b/static/js/copy_and_paste.js
index 0976d370db..598272f70d 100644
--- a/static/js/copy_and_paste.js
+++ b/static/js/copy_and_paste.js
@@ -1,3 +1,5 @@
+"use strict";
+
 const TurndownService = require("turndown/lib/turndown.cjs.js");
 
 function find_boundary_tr(initial_tr, iterate_row) {
diff --git a/static/js/csrf.js b/static/js/csrf.js
index cb237511d8..ec4d26d956 100644
--- a/static/js/csrf.js
+++ b/static/js/csrf.js
@@ -1,3 +1,5 @@
+"use strict";
+
 let csrf_token;
 $(() => {
     // This requires that we used Jinja2's {% csrf_input %} somewhere on the page.
diff --git a/static/js/drafts.js b/static/js/drafts.js
index f4f491416f..5a890a48fe 100644
--- a/static/js/drafts.js
+++ b/static/js/drafts.js
@@ -1,3 +1,5 @@
+"use strict";
+
 const Handlebars = require("handlebars/runtime");
 const XDate = require("xdate");
 
diff --git a/static/js/dropdown_list_widget.js b/static/js/dropdown_list_widget.js
index 9c5cb55768..c0a357d540 100644
--- a/static/js/dropdown_list_widget.js
+++ b/static/js/dropdown_list_widget.js
@@ -1,3 +1,5 @@
+"use strict";
+
 const DropdownListWidget = function (opts) {
     const init = () => {
         // Run basic sanity checks on opts, and set up sane defaults.
diff --git a/static/js/echo.js b/static/js/echo.js
index 4b7dbebcee..9cf9df9db7 100644
--- a/static/js/echo.js
+++ b/static/js/echo.js
@@ -1,3 +1,5 @@
+"use strict";
+
 const util = require("./util");
 // Docs: https://zulip.readthedocs.io/en/latest/subsystems/sending-messages.html
 
diff --git a/static/js/emoji_picker.js b/static/js/emoji_picker.js
index f2240724f0..af9deb0fb3 100644
--- a/static/js/emoji_picker.js
+++ b/static/js/emoji_picker.js
@@ -1,3 +1,5 @@
+"use strict";
+
 const emoji_codes = require("../generated/emoji/emoji_codes.json");
 const emoji = require("../shared/js/emoji");
 const typeahead = require("../shared/js/typeahead");
diff --git a/static/js/favicon.js b/static/js/favicon.js
index 773fdfa6b0..23db6e9534 100644
--- a/static/js/favicon.js
+++ b/static/js/favicon.js
@@ -1,3 +1,5 @@
+"use strict";
+
 exports.set = function (url) {
     $("#favicon").attr("href", url);
 };
diff --git a/static/js/feature_flags.js b/static/js/feature_flags.js
index af35ee5290..ae76281c87 100644
--- a/static/js/feature_flags.js
+++ b/static/js/feature_flags.js
@@ -1,3 +1,5 @@
+"use strict";
+
 // The features below have all settled into their final states and the flags
 // below can be removed when we get a chance.
 exports.reminders_in_message_action_menu = false;
diff --git a/static/js/feedback_widget.js b/static/js/feedback_widget.js
index c25293910a..7527138013 100644
--- a/static/js/feedback_widget.js
+++ b/static/js/feedback_widget.js
@@ -1,3 +1,5 @@
+"use strict";
+
 const render_feedback_container = require("../templates/feedback_container.hbs");
 
 /*
diff --git a/static/js/fetch_status.js b/static/js/fetch_status.js
index 77dd50eb61..09428e35c1 100644
--- a/static/js/fetch_status.js
+++ b/static/js/fetch_status.js
@@ -1,3 +1,5 @@
+"use strict";
+
 function max_id_for_messages(messages) {
     let max_id = 0;
     for (const msg of messages) {
diff --git a/static/js/filter.js b/static/js/filter.js
index 56e1ed4fea..2acf93bb16 100644
--- a/static/js/filter.js
+++ b/static/js/filter.js
@@ -1,3 +1,5 @@
+"use strict";
+
 const Handlebars = require("handlebars/runtime");
 const _ = require("lodash");
 
diff --git a/static/js/floating_recipient_bar.js b/static/js/floating_recipient_bar.js
index 3ed40e0905..9b50513d26 100644
--- a/static/js/floating_recipient_bar.js
+++ b/static/js/floating_recipient_bar.js
@@ -1,3 +1,5 @@
+"use strict";
+
 const XDate = require("xdate");
 
 let is_floating_recipient_bar_showing = false;
diff --git a/static/js/gear_menu.js b/static/js/gear_menu.js
index bd812337de..89e15c4001 100644
--- a/static/js/gear_menu.js
+++ b/static/js/gear_menu.js
@@ -1,3 +1,5 @@
+"use strict";
+
 /*
 For various historical reasons there isn't one
 single chunk of code that really makes our gear
diff --git a/static/js/hash_util.js b/static/js/hash_util.js
index 9a55ae5094..1964a32b55 100644
--- a/static/js/hash_util.js
+++ b/static/js/hash_util.js
@@ -1,3 +1,5 @@
+"use strict";
+
 exports.get_hash_category = function (hash) {
     // given "#streams/subscribed", returns "streams"
     return hash ? hash.replace(/^#/, "").split(/\//)[0] : "";
diff --git a/static/js/hashchange.js b/static/js/hashchange.js
index 728aba659b..9d06d2e03f 100644
--- a/static/js/hashchange.js
+++ b/static/js/hashchange.js
@@ -1,3 +1,5 @@
+"use strict";
+
 // Read https://zulip.readthedocs.io/en/latest/subsystems/hashchange-system.html
 // or locally: docs/subsystems/hashchange-system.md
 let changing_hash = false;
diff --git a/static/js/hotkey.js b/static/js/hotkey.js
index 528bf4663f..ae71d702cd 100644
--- a/static/js/hotkey.js
+++ b/static/js/hotkey.js
@@ -1,3 +1,5 @@
+"use strict";
+
 const emoji = require("../shared/js/emoji");
 
 function do_narrow_action(action) {
diff --git a/static/js/hotspots.js b/static/js/hotspots.js
index aa15ee6eff..a926e69836 100644
--- a/static/js/hotspots.js
+++ b/static/js/hotspots.js
@@ -1,3 +1,5 @@
+"use strict";
+
 const _ = require("lodash");
 
 const render_hotspot_overlay = require("../templates/hotspot_overlay.hbs");
diff --git a/static/js/huddle_data.js b/static/js/huddle_data.js
index a4ee46cac7..20a030fb7e 100644
--- a/static/js/huddle_data.js
+++ b/static/js/huddle_data.js
@@ -1,3 +1,5 @@
+"use strict";
+
 const _ = require("lodash");
 
 const huddle_timestamps = new Map();
diff --git a/static/js/info_overlay.js b/static/js/info_overlay.js
index ad400711f9..8f47f080da 100644
--- a/static/js/info_overlay.js
+++ b/static/js/info_overlay.js
@@ -1,3 +1,5 @@
+"use strict";
+
 // Make it explicit that our toggler is undefined until
 // set_up_toggler is called.
 exports.toggler = undefined;
diff --git a/static/js/input_pill.js b/static/js/input_pill.js
index 7826a1da27..0b47eda3de 100644
--- a/static/js/input_pill.js
+++ b/static/js/input_pill.js
@@ -1,3 +1,5 @@
+"use strict";
+
 const render_input_pill = require("../templates/input_pill.hbs");
 
 // See https://zulip.readthedocs.io/en/latest/subsystems/input-pills.html
diff --git a/static/js/invite.js b/static/js/invite.js
index 1db31bdab9..10bd4aba5c 100644
--- a/static/js/invite.js
+++ b/static/js/invite.js
@@ -1,3 +1,5 @@
+"use strict";
+
 const autosize = require("autosize");
 
 const render_invitation_failed_error = require("../templates/invitation_failed_error.hbs");
diff --git a/static/js/keydown_util.js b/static/js/keydown_util.js
index 0ebce06163..92ec7bde73 100644
--- a/static/js/keydown_util.js
+++ b/static/js/keydown_util.js
@@ -1,3 +1,5 @@
+"use strict";
+
 /*
     See hotkey.js for handlers that are more app-wide.
 */
diff --git a/static/js/lightbox.js b/static/js/lightbox.js
index 404ff21890..050af75a12 100644
--- a/static/js/lightbox.js
+++ b/static/js/lightbox.js
@@ -1,3 +1,5 @@
+"use strict";
+
 let is_open = false;
 // the asset map is a map of all retrieved images and YouTube videos that are
 // memoized instead of being looked up multiple times.
diff --git a/static/js/lightbox_canvas.js b/static/js/lightbox_canvas.js
index d4a79908fb..4f6d7caecb 100644
--- a/static/js/lightbox_canvas.js
+++ b/static/js/lightbox_canvas.js
@@ -1,3 +1,5 @@
+"use strict";
+
 const funcs = {
     setZoom(meta, zoom) {
         // condition to handle zooming event by zoom hotkeys
diff --git a/static/js/list_cursor.js b/static/js/list_cursor.js
index 1256fd8e7d..a40edc82cb 100644
--- a/static/js/list_cursor.js
+++ b/static/js/list_cursor.js
@@ -1,3 +1,5 @@
+"use strict";
+
 class ListCursor {
     constructor({highlight_class, list}) {
         const config_ok =
diff --git a/static/js/list_render.js b/static/js/list_render.js
index b317b4f316..b282931285 100644
--- a/static/js/list_render.js
+++ b/static/js/list_render.js
@@ -1,3 +1,5 @@
+"use strict";
+
 const DEFAULTS = {
     INITIAL_RENDER_COUNT: 80,
     LOAD_COUNT: 20,
diff --git a/static/js/list_util.js b/static/js/list_util.js
index 5aeefeba56..e82b7d0838 100644
--- a/static/js/list_util.js
+++ b/static/js/list_util.js
@@ -1,3 +1,5 @@
+"use strict";
+
 const list_selectors = ["#stream_filters", "#global_filters", "#user_presences"];
 
 exports.inside_list = function (e) {
diff --git a/static/js/loading.js b/static/js/loading.js
index 2f31c43193..e1b2f647fc 100644
--- a/static/js/loading.js
+++ b/static/js/loading.js
@@ -1,3 +1,5 @@
+"use strict";
+
 const render_loader = require("../templates/loader.hbs");
 
 exports.make_indicator = function (outer_container, opts) {
diff --git a/static/js/local_message.js b/static/js/local_message.js
index 1df8abca5f..395351d39d 100644
--- a/static/js/local_message.js
+++ b/static/js/local_message.js
@@ -1,3 +1,5 @@
+"use strict";
+
 const XDate = require("xdate");
 
 function truncate_precision(float) {
diff --git a/static/js/localstorage.js b/static/js/localstorage.js
index 25081605cd..421669cd0a 100644
--- a/static/js/localstorage.js
+++ b/static/js/localstorage.js
@@ -1,3 +1,5 @@
+"use strict";
+
 const ls = {
     // parse JSON without throwing an error.
     parseJSON(str) {
diff --git a/static/js/markdown.js b/static/js/markdown.js
index 9d974b6b68..1e80ac812e 100644
--- a/static/js/markdown.js
+++ b/static/js/markdown.js
@@ -1,3 +1,5 @@
+"use strict";
+
 const katex = require("katex/dist/katex.min.js");
 const _ = require("lodash");
 const moment = require("moment");
diff --git a/static/js/markdown_config.js b/static/js/markdown_config.js
index 718cd26c59..116b96a448 100644
--- a/static/js/markdown_config.js
+++ b/static/js/markdown_config.js
@@ -1,3 +1,5 @@
+"use strict";
+
 /*
     This config is in a separate file for partly
     tactical reasons.  We want the webapp to
diff --git a/static/js/message_edit.js b/static/js/message_edit.js
index 79aa1a9f8c..ee8988c880 100644
--- a/static/js/message_edit.js
+++ b/static/js/message_edit.js
@@ -1,3 +1,5 @@
+"use strict";
+
 const ClipboardJS = require("clipboard");
 const XDate = require("xdate");
 
diff --git a/static/js/message_edit_history.js b/static/js/message_edit_history.js
index 00192d3544..7b05bccc24 100644
--- a/static/js/message_edit_history.js
+++ b/static/js/message_edit_history.js
@@ -1,3 +1,5 @@
+"use strict";
+
 const XDate = require("xdate");
 
 const render_message_edit_history = require("../templates/message_edit_history.hbs");
diff --git a/static/js/message_events.js b/static/js/message_events.js
index 0d2bfe4639..6d3e9a255a 100644
--- a/static/js/message_events.js
+++ b/static/js/message_events.js
@@ -1,3 +1,5 @@
+"use strict";
+
 const huddle_data = require("./huddle_data");
 const util = require("./util");
 
diff --git a/static/js/message_fetch.js b/static/js/message_fetch.js
index f94fa7905a..a9d04e0dd4 100644
--- a/static/js/message_fetch.js
+++ b/static/js/message_fetch.js
@@ -1,3 +1,5 @@
+"use strict";
+
 const huddle_data = require("./huddle_data");
 
 const consts = {
diff --git a/static/js/message_flags.js b/static/js/message_flags.js
index f3530fd4e6..d4c36a8c74 100644
--- a/static/js/message_flags.js
+++ b/static/js/message_flags.js
@@ -1,3 +1,5 @@
+"use strict";
+
 const _ = require("lodash");
 
 function send_flag_update(message, flag, op) {
diff --git a/static/js/message_list.js b/static/js/message_list.js
index 4ee287b3c7..d844f2292e 100644
--- a/static/js/message_list.js
+++ b/static/js/message_list.js
@@ -1,3 +1,5 @@
+"use strict";
+
 const autosize = require("autosize");
 
 exports.narrowed = undefined;
diff --git a/static/js/message_list_data.js b/static/js/message_list_data.js
index fefac29b02..9684db08c9 100644
--- a/static/js/message_list_data.js
+++ b/static/js/message_list_data.js
@@ -1,3 +1,5 @@
+"use strict";
+
 const _ = require("lodash");
 
 const util = require("./util");
diff --git a/static/js/message_list_view.js b/static/js/message_list_view.js
index 668a6ed24c..5fa7dadc6f 100644
--- a/static/js/message_list_view.js
+++ b/static/js/message_list_view.js
@@ -1,3 +1,5 @@
+"use strict";
+
 const _ = require("lodash");
 const XDate = require("xdate");
 
diff --git a/static/js/message_live_update.js b/static/js/message_live_update.js
index c0b86ee61c..2e0187c232 100644
--- a/static/js/message_live_update.js
+++ b/static/js/message_live_update.js
@@ -1,3 +1,5 @@
+"use strict";
+
 function rerender_messages_view() {
     for (const list of [home_msg_list, message_list.narrowed, message_list.all]) {
         if (list === undefined) {
diff --git a/static/js/message_scroll.js b/static/js/message_scroll.js
index 2aff03015b..2376408af4 100644
--- a/static/js/message_scroll.js
+++ b/static/js/message_scroll.js
@@ -1,3 +1,5 @@
+"use strict";
+
 const _ = require("lodash");
 
 let actively_scrolling = false;
diff --git a/static/js/message_store.js b/static/js/message_store.js
index 1e88d319f9..812a0e9416 100644
--- a/static/js/message_store.js
+++ b/static/js/message_store.js
@@ -1,3 +1,5 @@
+"use strict";
+
 const util = require("./util");
 
 const stored_messages = new Map();
diff --git a/static/js/message_util.js b/static/js/message_util.js
index b57eb3a849..6ec9d85b4a 100644
--- a/static/js/message_util.js
+++ b/static/js/message_util.js
@@ -1,3 +1,5 @@
+"use strict";
+
 exports.do_unread_count_updates = function do_unread_count_updates(messages) {
     unread.process_loaded_messages(messages);
     unread_ui.update_unread_counts();
diff --git a/static/js/message_view_header.js b/static/js/message_view_header.js
index 37d7825692..a3b970b495 100644
--- a/static/js/message_view_header.js
+++ b/static/js/message_view_header.js
@@ -1,3 +1,5 @@
+"use strict";
+
 const render_message_view_header = require("../templates/message_view_header.hbs");
 
 const rendered_markdown = require("./rendered_markdown");
diff --git a/static/js/message_viewport.js b/static/js/message_viewport.js
index 1d052efc2e..58240c8257 100644
--- a/static/js/message_viewport.js
+++ b/static/js/message_viewport.js
@@ -1,3 +1,5 @@
+"use strict";
+
 const util = require("./util");
 
 let jwindow;
diff --git a/static/js/muting.js b/static/js/muting.js
index 0f45dc77b7..c60ed41eb4 100644
--- a/static/js/muting.js
+++ b/static/js/muting.js
@@ -1,3 +1,5 @@
+"use strict";
+
 const XDate = require("xdate");
 
 const FoldDict = require("./fold_dict").FoldDict;
diff --git a/static/js/muting_ui.js b/static/js/muting_ui.js
index 5deb4cf775..a625878736 100644
--- a/static/js/muting_ui.js
+++ b/static/js/muting_ui.js
@@ -1,3 +1,5 @@
+"use strict";
+
 const render_muted_topic_ui_row = require("../templates/muted_topic_ui_row.hbs");
 const render_topic_muted = require("../templates/topic_muted.hbs");
 
diff --git a/static/js/narrow.js b/static/js/narrow.js
index deb1fb5f05..3cdca87142 100644
--- a/static/js/narrow.js
+++ b/static/js/narrow.js
@@ -1,3 +1,5 @@
+"use strict";
+
 const util = require("./util");
 
 let unnarrow_times;
diff --git a/static/js/narrow_state.js b/static/js/narrow_state.js
index e244df99f2..3b45151429 100644
--- a/static/js/narrow_state.js
+++ b/static/js/narrow_state.js
@@ -1,3 +1,5 @@
+"use strict";
+
 let current_filter;
 
 exports.reset_current_filter = function () {
diff --git a/static/js/navigate.js b/static/js/navigate.js
index f353202dd0..1eddcda530 100644
--- a/static/js/navigate.js
+++ b/static/js/navigate.js
@@ -1,3 +1,5 @@
+"use strict";
+
 function go_to_row(msg_id) {
     current_msg_list.select_id(msg_id, {then_scroll: true, from_scroll: true});
 }
diff --git a/static/js/night_mode.js b/static/js/night_mode.js
index 3b32690ec1..9cbf9157a9 100644
--- a/static/js/night_mode.js
+++ b/static/js/night_mode.js
@@ -1,3 +1,5 @@
+"use strict";
+
 exports.enable = function () {
     $("body").removeClass("color-scheme-automatic").addClass("night-mode");
 };
diff --git a/static/js/notifications.js b/static/js/notifications.js
index 7664c8330e..610bba75c3 100644
--- a/static/js/notifications.js
+++ b/static/js/notifications.js
@@ -1,3 +1,5 @@
+"use strict";
+
 const _ = require("lodash");
 
 const render_compose_notification = require("../templates/compose_notification.hbs");
diff --git a/static/js/overlays.js b/static/js/overlays.js
index f23acad583..a93d4baf15 100644
--- a/static/js/overlays.js
+++ b/static/js/overlays.js
@@ -1,3 +1,5 @@
+"use strict";
+
 let active_overlay;
 let close_handler;
 let open_overlay_name;
diff --git a/static/js/padded_widget.js b/static/js/padded_widget.js
index ee4611bd6e..3a74104e90 100644
--- a/static/js/padded_widget.js
+++ b/static/js/padded_widget.js
@@ -1,3 +1,5 @@
+"use strict";
+
 exports.update_padding = function (opts) {
     const content = $(opts.content_sel);
     const padding = $(opts.padding_sel);
diff --git a/static/js/page_params.js b/static/js/page_params.js
index 6dc03b148f..8364c82540 100644
--- a/static/js/page_params.js
+++ b/static/js/page_params.js
@@ -1,3 +1,5 @@
+"use strict";
+
 /* global __webpack_public_path__:writable */
 
 const t1 = performance.now();
diff --git a/static/js/panels.js b/static/js/panels.js
index f04c83b138..946d791b40 100644
--- a/static/js/panels.js
+++ b/static/js/panels.js
@@ -1,3 +1,5 @@
+"use strict";
+
 const util = require("./util");
 
 const resize_app = function () {
diff --git a/static/js/people.js b/static/js/people.js
index 1ee53834ef..8d5e7c5cfa 100644
--- a/static/js/people.js
+++ b/static/js/people.js
@@ -1,3 +1,5 @@
+"use strict";
+
 const md5 = require("blueimp-md5");
 const _ = require("lodash");
 const moment = require("moment-timezone");
diff --git a/static/js/pm_conversations.js b/static/js/pm_conversations.js
index b6d17378f2..a87d019b6d 100644
--- a/static/js/pm_conversations.js
+++ b/static/js/pm_conversations.js
@@ -1,3 +1,5 @@
+"use strict";
+
 const FoldDict = require("./fold_dict").FoldDict;
 
 const partners = new Set();
diff --git a/static/js/pm_list.js b/static/js/pm_list.js
index 1ede45fcef..a9eb626d8e 100644
--- a/static/js/pm_list.js
+++ b/static/js/pm_list.js
@@ -1,3 +1,5 @@
+"use strict";
+
 let prior_dom;
 let private_messages_open = false;
 
diff --git a/static/js/pm_list_dom.js b/static/js/pm_list_dom.js
index 95250b7005..bf0afde78f 100644
--- a/static/js/pm_list_dom.js
+++ b/static/js/pm_list_dom.js
@@ -1,3 +1,5 @@
+"use strict";
+
 const _ = require("lodash");
 
 const render_pm_list_item = require("../templates/pm_list_item.hbs");
diff --git a/static/js/poll_widget.js b/static/js/poll_widget.js
index 10db32e8bf..d5f9d2476f 100644
--- a/static/js/poll_widget.js
+++ b/static/js/poll_widget.js
@@ -1,3 +1,5 @@
+"use strict";
+
 const render_widgets_poll_widget = require("../templates/widgets/poll_widget.hbs");
 const render_widgets_poll_widget_results = require("../templates/widgets/poll_widget_results.hbs");
 
diff --git a/static/js/popovers.js b/static/js/popovers.js
index 86d5401aba..ba61bc7952 100644
--- a/static/js/popovers.js
+++ b/static/js/popovers.js
@@ -1,3 +1,5 @@
+"use strict";
+
 const ClipboardJS = require("clipboard");
 const confirmDatePlugin = require("flatpickr/dist/plugins/confirmDate/confirmDate.js");
 const moment = require("moment");
diff --git a/static/js/portico/confirm-preregistrationuser.js b/static/js/portico/confirm-preregistrationuser.js
index 10d2f883ff..61c43376d0 100644
--- a/static/js/portico/confirm-preregistrationuser.js
+++ b/static/js/portico/confirm-preregistrationuser.js
@@ -1,3 +1,5 @@
+"use strict";
+
 $(() => {
     $("#register").trigger("submit");
 });
diff --git a/static/js/portico/desktop-login.js b/static/js/portico/desktop-login.js
index 52da6cba96..66dba54a34 100644
--- a/static/js/portico/desktop-login.js
+++ b/static/js/portico/desktop-login.js
@@ -1,3 +1,5 @@
+"use strict";
+
 document.querySelector("#form").addEventListener("submit", () => {
     document.querySelector("#bad-token").hidden = false;
 });
diff --git a/static/js/portico/desktop-redirect.js b/static/js/portico/desktop-redirect.js
index 1a60d9d60d..164d8fa706 100644
--- a/static/js/portico/desktop-redirect.js
+++ b/static/js/portico/desktop-redirect.js
@@ -1,3 +1,5 @@
+"use strict";
+
 const ClipboardJS = require("clipboard");
 
 new ClipboardJS("#copy");
diff --git a/static/js/portico/dev-login.js b/static/js/portico/dev-login.js
index 5e1891b92c..265ef72b11 100644
--- a/static/js/portico/dev-login.js
+++ b/static/js/portico/dev-login.js
@@ -1,3 +1,5 @@
+"use strict";
+
 $(() => {
     // This code will be executed when the user visits /login and
     // dev_login.html is rendered.
diff --git a/static/js/portico/email_log.js b/static/js/portico/email_log.js
index 848111caba..d5e9ac6aec 100644
--- a/static/js/portico/email_log.js
+++ b/static/js/portico/email_log.js
@@ -1,3 +1,5 @@
+"use strict";
+
 $(() => {
     // This code will be executed when the user visits /emails in
     // development mode and email_log.html is rendered.
diff --git a/static/js/portico/header.js b/static/js/portico/header.js
index 4043020b89..2bf68dcc37 100644
--- a/static/js/portico/header.js
+++ b/static/js/portico/header.js
@@ -1,3 +1,5 @@
+"use strict";
+
 $(() => {
     $(".portico-header li.logout").on("click", () => {
         $("#logout_form").trigger("submit");
diff --git a/static/js/portico/integrations_dev_panel.js b/static/js/portico/integrations_dev_panel.js
index d9fb21af40..b082c80298 100644
--- a/static/js/portico/integrations_dev_panel.js
+++ b/static/js/portico/integrations_dev_panel.js
@@ -1,3 +1,5 @@
+"use strict";
+
 // Main JavaScript file for the Integrations development panel at
 // /devtools/integrations.
 
diff --git a/static/js/portico/signup.js b/static/js/portico/signup.js
index 11328da994..9af27c452e 100644
--- a/static/js/portico/signup.js
+++ b/static/js/portico/signup.js
@@ -1,3 +1,5 @@
+"use strict";
+
 const moment = require("moment-timezone");
 
 $(() => {
diff --git a/static/js/presence.js b/static/js/presence.js
index 203fc41f9c..59cdd96c8c 100644
--- a/static/js/presence.js
+++ b/static/js/presence.js
@@ -1,3 +1,5 @@
+"use strict";
+
 const XDate = require("xdate");
 
 // This module just manages data.  See activity.js for
diff --git a/static/js/reactions.js b/static/js/reactions.js
index bb49c3e961..47a52b3fa2 100644
--- a/static/js/reactions.js
+++ b/static/js/reactions.js
@@ -1,3 +1,5 @@
+"use strict";
+
 const _ = require("lodash");
 
 const emoji = require("../shared/js/emoji");
diff --git a/static/js/ready.js b/static/js/ready.js
index 17f30f3b03..2aaef76ba1 100644
--- a/static/js/ready.js
+++ b/static/js/ready.js
@@ -1 +1,3 @@
+"use strict";
+
 $("#app-loading").addClass("loaded");
diff --git a/static/js/realm_icon.js b/static/js/realm_icon.js
index 9d12708b95..0467dccd18 100644
--- a/static/js/realm_icon.js
+++ b/static/js/realm_icon.js
@@ -1,3 +1,5 @@
+"use strict";
+
 exports.build_realm_icon_widget = function (upload_function) {
     const get_file_input = function () {
         return $("#realm-icon-upload-widget .image_file_input").expectOne();
diff --git a/static/js/realm_logo.js b/static/js/realm_logo.js
index 3dc78f70ed..f82221919e 100644
--- a/static/js/realm_logo.js
+++ b/static/js/realm_logo.js
@@ -1,3 +1,5 @@
+"use strict";
+
 const settings_config = require("./settings_config");
 
 exports.build_realm_logo_widget = function (upload_function, is_night) {
diff --git a/static/js/recent_senders.js b/static/js/recent_senders.js
index b450fc1e40..bd24a6e06e 100644
--- a/static/js/recent_senders.js
+++ b/static/js/recent_senders.js
@@ -1,3 +1,5 @@
+"use strict";
+
 const FoldDict = require("./fold_dict").FoldDict;
 
 // topic_senders[stream_id][topic_id][sender_id] = latest_message_id
diff --git a/static/js/recent_topics.js b/static/js/recent_topics.js
index d160ae08ef..3019a38721 100644
--- a/static/js/recent_topics.js
+++ b/static/js/recent_topics.js
@@ -1,3 +1,5 @@
+"use strict";
+
 const XDate = require("xdate");
 
 const render_recent_topic_row = require("../templates/recent_topic_row.hbs");
diff --git a/static/js/reload.js b/static/js/reload.js
index 62567557b3..d1c558da3e 100644
--- a/static/js/reload.js
+++ b/static/js/reload.js
@@ -1,3 +1,5 @@
+"use strict";
+
 const util = require("./util");
 // Read https://zulip.readthedocs.io/en/latest/subsystems/hashchange-system.html
 function preserve_state(send_after_reload, save_pointer, save_narrow, save_compose) {
diff --git a/static/js/reload_state.js b/static/js/reload_state.js
index 33ce867228..3e78804402 100644
--- a/static/js/reload_state.js
+++ b/static/js/reload_state.js
@@ -1,3 +1,5 @@
+"use strict";
+
 /*
     We want his module to load pretty early in the process
     of starting the app, so that people.js can load early.
diff --git a/static/js/reminder.js b/static/js/reminder.js
index bf336e7461..c8aedb940e 100644
--- a/static/js/reminder.js
+++ b/static/js/reminder.js
@@ -1,3 +1,5 @@
+"use strict";
+
 const moment = require("moment-timezone");
 
 const util = require("./util");
diff --git a/static/js/rendered_markdown.js b/static/js/rendered_markdown.js
index b15c7b0f1d..ef688fbd33 100644
--- a/static/js/rendered_markdown.js
+++ b/static/js/rendered_markdown.js
@@ -1,3 +1,5 @@
+"use strict";
+
 const moment = require("moment");
 
 /*
diff --git a/static/js/resize.js b/static/js/resize.js
index c3418b3d12..2e034aa84a 100644
--- a/static/js/resize.js
+++ b/static/js/resize.js
@@ -1,3 +1,5 @@
+"use strict";
+
 const autosize = require("autosize");
 
 const util = require("./util");
diff --git a/static/js/rows.js b/static/js/rows.js
index 01b67f4c27..0b160b07ad 100644
--- a/static/js/rows.js
+++ b/static/js/rows.js
@@ -1,3 +1,5 @@
+"use strict";
+
 // We don't need an andSelf() here because we already know
 // that our next element is *not* a message_row, so this
 // isn't going to end up empty unless we're at the bottom or top.
diff --git a/static/js/rtl.js b/static/js/rtl.js
index 6058928b5c..f1b8083c04 100644
--- a/static/js/rtl.js
+++ b/static/js/rtl.js
@@ -1,3 +1,5 @@
+"use strict";
+
 const util = require("./util");
 // How to determine the direction of a paragraph (P1-P3): https://www.unicode.org/reports/tr9/tr9-35.html#The_Paragraph_Level
 // Embedding level: https://www.unicode.org/reports/tr9/tr9-35.html#BD2
diff --git a/static/js/schema.js b/static/js/schema.js
index aee875ad5f..7210e607e5 100644
--- a/static/js/schema.js
+++ b/static/js/schema.js
@@ -1,3 +1,5 @@
+"use strict";
+
 /*
 
 These runtime schema validators are defensive and
diff --git a/static/js/scroll_bar.js b/static/js/scroll_bar.js
index 613898f555..cfd8b4a0aa 100644
--- a/static/js/scroll_bar.js
+++ b/static/js/scroll_bar.js
@@ -1,3 +1,5 @@
+"use strict";
+
 // A few of our width properties in zulip depend on the width of the
 // browser scrollbar that is generated at the far right side of the
 // page, which unfortunately varies depending on the browser and
diff --git a/static/js/scroll_util.js b/static/js/scroll_util.js
index 934a96baf3..360f2264ab 100644
--- a/static/js/scroll_util.js
+++ b/static/js/scroll_util.js
@@ -1,3 +1,5 @@
+"use strict";
+
 exports.scroll_delta = function (opts) {
     const elem_top = opts.elem_top;
     const container_height = opts.container_height;
diff --git a/static/js/search.js b/static/js/search.js
index b33b099d6d..3952dec9da 100644
--- a/static/js/search.js
+++ b/static/js/search.js
@@ -1,3 +1,5 @@
+"use strict";
+
 // Exported for unit testing
 exports.is_using_input_method = false;
 
diff --git a/static/js/search_pill.js b/static/js/search_pill.js
index 90c47e0503..3b9ecb807d 100644
--- a/static/js/search_pill.js
+++ b/static/js/search_pill.js
@@ -1,3 +1,5 @@
+"use strict";
+
 exports.create_item_from_search_string = function (search_string) {
     const operator = Filter.parse(search_string);
     const description = Filter.describe(operator);
diff --git a/static/js/search_pill_widget.js b/static/js/search_pill_widget.js
index 10fd2fcda2..4726ab2afa 100644
--- a/static/js/search_pill_widget.js
+++ b/static/js/search_pill_widget.js
@@ -1,3 +1,5 @@
+"use strict";
+
 exports.initialize = function () {
     if (!page_params.search_pills_enabled) {
         return;
diff --git a/static/js/search_suggestion.js b/static/js/search_suggestion.js
index d39aeeeace..f3b5518d2f 100644
--- a/static/js/search_suggestion.js
+++ b/static/js/search_suggestion.js
@@ -1,3 +1,5 @@
+"use strict";
+
 const Handlebars = require("handlebars/runtime");
 
 const huddle_data = require("./huddle_data");
diff --git a/static/js/search_util.js b/static/js/search_util.js
index fc597ab97c..bf75258342 100644
--- a/static/js/search_util.js
+++ b/static/js/search_util.js
@@ -1,3 +1,5 @@
+"use strict";
+
 exports.get_search_terms = function (input) {
     const search_terms = input
         .toLowerCase()
diff --git a/static/js/sent_messages.js b/static/js/sent_messages.js
index d9f4784c32..c2e9702a2b 100644
--- a/static/js/sent_messages.js
+++ b/static/js/sent_messages.js
@@ -1,3 +1,5 @@
+"use strict";
+
 exports.messages = new Map();
 
 exports.reset_id_state = function () {
diff --git a/static/js/server_events.js b/static/js/server_events.js
index 8b4a689b12..ab0d606d6c 100644
--- a/static/js/server_events.js
+++ b/static/js/server_events.js
@@ -1,3 +1,5 @@
+"use strict";
+
 const _ = require("lodash");
 // Docs: https://zulip.readthedocs.io/en/latest/subsystems/events-system.html
 
diff --git a/static/js/server_events_dispatch.js b/static/js/server_events_dispatch.js
index d7f4d08f6f..4497881d72 100644
--- a/static/js/server_events_dispatch.js
+++ b/static/js/server_events_dispatch.js
@@ -1,3 +1,5 @@
+"use strict";
+
 const emoji = require("../shared/js/emoji");
 
 const settings_config = require("./settings_config");
diff --git a/static/js/settings.js b/static/js/settings.js
index 2e602c9770..2bded384fb 100644
--- a/static/js/settings.js
+++ b/static/js/settings.js
@@ -1,3 +1,5 @@
+"use strict";
+
 const moment = require("moment-timezone");
 
 const render_settings_tab = require("../templates/settings_tab.hbs");
diff --git a/static/js/settings_account.js b/static/js/settings_account.js
index f963c2ed57..3dd93a8306 100644
--- a/static/js/settings_account.js
+++ b/static/js/settings_account.js
@@ -1,3 +1,5 @@
+"use strict";
+
 const _ = require("lodash");
 
 const render_settings_api_key_modal = require("../templates/settings/api_key_modal.hbs");
diff --git a/static/js/settings_bots.js b/static/js/settings_bots.js
index eccfe85643..7f9021aaea 100644
--- a/static/js/settings_bots.js
+++ b/static/js/settings_bots.js
@@ -1,3 +1,5 @@
+"use strict";
+
 const ClipboardJS = require("clipboard");
 
 const render_bot_avatar_row = require("../templates/bot_avatar_row.hbs");
diff --git a/static/js/settings_config.js b/static/js/settings_config.js
index 05f96b7d4a..3ccfe2789b 100644
--- a/static/js/settings_config.js
+++ b/static/js/settings_config.js
@@ -1,3 +1,5 @@
+"use strict";
+
 /*
     This file contains translations between the integer values used in
     the Zulip API to describe values in dropdowns, radio buttons, and
diff --git a/static/js/settings_data.js b/static/js/settings_data.js
index b8637f71cd..f0714f7da9 100644
--- a/static/js/settings_data.js
+++ b/static/js/settings_data.js
@@ -1,3 +1,5 @@
+"use strict";
+
 const settings_config = require("./settings_config");
 
 /*
diff --git a/static/js/settings_display.js b/static/js/settings_display.js
index 15b7d83b2c..edcdc500d1 100644
--- a/static/js/settings_display.js
+++ b/static/js/settings_display.js
@@ -1,3 +1,5 @@
+"use strict";
+
 const emojisets = require("./emojisets.js");
 const settings_config = require("./settings_config");
 
diff --git a/static/js/settings_emoji.js b/static/js/settings_emoji.js
index 8f7b71fbc2..5e255e8a34 100644
--- a/static/js/settings_emoji.js
+++ b/static/js/settings_emoji.js
@@ -1,3 +1,5 @@
+"use strict";
+
 const emoji = require("../shared/js/emoji");
 const render_admin_emoji_list = require("../templates/admin_emoji_list.hbs");
 const render_settings_emoji_settings_tip = require("../templates/settings/emoji_settings_tip.hbs");
diff --git a/static/js/settings_exports.js b/static/js/settings_exports.js
index 385e3601b8..bdd79a0da7 100644
--- a/static/js/settings_exports.js
+++ b/static/js/settings_exports.js
@@ -1,3 +1,5 @@
+"use strict";
+
 const XDate = require("xdate");
 
 const render_admin_export_list = require("../templates/admin_export_list.hbs");
diff --git a/static/js/settings_invites.js b/static/js/settings_invites.js
index c67bb75bc1..271a0daa54 100644
--- a/static/js/settings_invites.js
+++ b/static/js/settings_invites.js
@@ -1,3 +1,5 @@
+"use strict";
+
 const render_admin_invites_list = require("../templates/admin_invites_list.hbs");
 const render_settings_revoke_invite_modal = require("../templates/settings/revoke_invite_modal.hbs");
 
diff --git a/static/js/settings_linkifiers.js b/static/js/settings_linkifiers.js
index 56f283a502..78d12627fc 100644
--- a/static/js/settings_linkifiers.js
+++ b/static/js/settings_linkifiers.js
@@ -1,3 +1,5 @@
+"use strict";
+
 const render_admin_filter_list = require("../templates/admin_filter_list.hbs");
 
 const meta = {
diff --git a/static/js/settings_muting.js b/static/js/settings_muting.js
index 96b7e65178..8d9f39b270 100644
--- a/static/js/settings_muting.js
+++ b/static/js/settings_muting.js
@@ -1,3 +1,5 @@
+"use strict";
+
 exports.loaded = false;
 
 exports.set_up = function () {
diff --git a/static/js/settings_notifications.js b/static/js/settings_notifications.js
index a5e2923d72..9f693481d4 100644
--- a/static/js/settings_notifications.js
+++ b/static/js/settings_notifications.js
@@ -1,3 +1,5 @@
+"use strict";
+
 const render_stream_specific_notification_row = require("../templates/settings/stream_specific_notification_row.hbs");
 
 const settings_config = require("./settings_config");
diff --git a/static/js/settings_org.js b/static/js/settings_org.js
index 1ae124cb69..3fac66c795 100644
--- a/static/js/settings_org.js
+++ b/static/js/settings_org.js
@@ -1,3 +1,5 @@
+"use strict";
+
 const pygments_data = require("../generated/pygments_data.json");
 const render_settings_admin_auth_methods_list = require("../templates/settings/admin_auth_methods_list.hbs");
 const render_settings_admin_realm_domains_list = require("../templates/settings/admin_realm_domains_list.hbs");
diff --git a/static/js/settings_panel_menu.js b/static/js/settings_panel_menu.js
index eff6eaf091..1feaad20b0 100644
--- a/static/js/settings_panel_menu.js
+++ b/static/js/settings_panel_menu.js
@@ -1,3 +1,5 @@
+"use strict";
+
 exports.mobile_deactivate_section = function () {
     const $settings_overlay_container = $("#settings_overlay_container");
     $settings_overlay_container.find(".right").removeClass("show");
diff --git a/static/js/settings_profile_fields.js b/static/js/settings_profile_fields.js
index fed6f2004d..11b2f6384c 100644
--- a/static/js/settings_profile_fields.js
+++ b/static/js/settings_profile_fields.js
@@ -1,3 +1,5 @@
+"use strict";
+
 const Sortable = require("sortablejs").default;
 
 const render_admin_profile_field_list = require("../templates/admin_profile_field_list.hbs");
diff --git a/static/js/settings_sections.js b/static/js/settings_sections.js
index 9f729d47e8..6d018fbc51 100644
--- a/static/js/settings_sections.js
+++ b/static/js/settings_sections.js
@@ -1,3 +1,5 @@
+"use strict";
+
 const load_func_dict = new Map(); // group -> function
 const loaded_groups = new Set();
 
diff --git a/static/js/settings_streams.js b/static/js/settings_streams.js
index 1203cd54a9..4a2d5368e3 100644
--- a/static/js/settings_streams.js
+++ b/static/js/settings_streams.js
@@ -1,3 +1,5 @@
+"use strict";
+
 const render_admin_default_streams_list = require("../templates/admin_default_streams_list.hbs");
 
 const meta = {
diff --git a/static/js/settings_toggle.js b/static/js/settings_toggle.js
index 0aece5a231..53874000f6 100644
--- a/static/js/settings_toggle.js
+++ b/static/js/settings_toggle.js
@@ -1,3 +1,5 @@
+"use strict";
+
 let toggler;
 
 exports.highlight_toggle = function (tab_name) {
diff --git a/static/js/settings_ui.js b/static/js/settings_ui.js
index 24aa69320d..d789e33d22 100644
--- a/static/js/settings_ui.js
+++ b/static/js/settings_ui.js
@@ -1,3 +1,5 @@
+"use strict";
+
 exports.display_checkmark = function ($elem) {
     const check_mark = document.createElement("img");
     check_mark.src = "/static/images/checkbox-green.svg";
diff --git a/static/js/settings_user_groups.js b/static/js/settings_user_groups.js
index 3ab185bd00..e65992327b 100644
--- a/static/js/settings_user_groups.js
+++ b/static/js/settings_user_groups.js
@@ -1,3 +1,5 @@
+"use strict";
+
 const _ = require("lodash");
 
 const render_admin_user_group_list = require("../templates/admin_user_group_list.hbs");
diff --git a/static/js/settings_users.js b/static/js/settings_users.js
index e6c70df210..36eb1c0ea7 100644
--- a/static/js/settings_users.js
+++ b/static/js/settings_users.js
@@ -1,3 +1,5 @@
+"use strict";
+
 const render_admin_bot_form = require("../templates/admin_bot_form.hbs");
 const render_admin_human_form = require("../templates/admin_human_form.hbs");
 const render_admin_user_list = require("../templates/admin_user_list.hbs");
diff --git a/static/js/setup.js b/static/js/setup.js
index 5daaf8814f..73a8601468 100644
--- a/static/js/setup.js
+++ b/static/js/setup.js
@@ -1,3 +1,5 @@
+"use strict";
+
 const util = require("./util");
 // Miscellaneous early setup.
 
diff --git a/static/js/spoilers.js b/static/js/spoilers.js
index c485a435da..96d4571756 100644
--- a/static/js/spoilers.js
+++ b/static/js/spoilers.js
@@ -1,3 +1,5 @@
+"use strict";
+
 function collapse_spoiler(spoiler) {
     const spoiler_height = spoiler.height();
 
diff --git a/static/js/starred_messages.js b/static/js/starred_messages.js
index ad8ace1f1a..56e114321f 100644
--- a/static/js/starred_messages.js
+++ b/static/js/starred_messages.js
@@ -1,3 +1,5 @@
+"use strict";
+
 exports.ids = new Set();
 
 exports.initialize = function () {
diff --git a/static/js/stats/stats.js b/static/js/stats/stats.js
index 17dd0c42ab..9eb39c1d40 100644
--- a/static/js/stats/stats.js
+++ b/static/js/stats/stats.js
@@ -1,3 +1,5 @@
+"use strict";
+
 const Plotly = require("plotly.js/lib/core");
 
 Plotly.register([require("plotly.js/lib/bar"), require("plotly.js/lib/pie")]);
diff --git a/static/js/stream_color.js b/static/js/stream_color.js
index 7905675b4c..5194671df3 100644
--- a/static/js/stream_color.js
+++ b/static/js/stream_color.js
@@ -1,3 +1,5 @@
+"use strict";
+
 const _ = require("lodash");
 
 exports.default_color = "#c2c2c2";
diff --git a/static/js/stream_create.js b/static/js/stream_create.js
index 3ce42f9cba..6730623a87 100644
--- a/static/js/stream_create.js
+++ b/static/js/stream_create.js
@@ -1,3 +1,5 @@
+"use strict";
+
 const render_announce_stream_docs = require("../templates/announce_stream_docs.hbs");
 const render_new_stream_users = require("../templates/new_stream_users.hbs");
 const render_subscription_invites_warning_modal = require("../templates/subscription_invites_warning_modal.hbs");
diff --git a/static/js/stream_data.js b/static/js/stream_data.js
index 00c6e4599b..00d80af889 100644
--- a/static/js/stream_data.js
+++ b/static/js/stream_data.js
@@ -1,3 +1,5 @@
+"use strict";
+
 const FoldDict = require("./fold_dict").FoldDict;
 const LazySet = require("./lazy_set").LazySet;
 const settings_config = require("./settings_config");
diff --git a/static/js/stream_edit.js b/static/js/stream_edit.js
index 3e64be46fe..256094ce6a 100644
--- a/static/js/stream_edit.js
+++ b/static/js/stream_edit.js
@@ -1,3 +1,5 @@
+"use strict";
+
 const render_settings_deactivation_stream_modal = require("../templates/settings/deactivation_stream_modal.hbs");
 const render_stream_member_list_entry = require("../templates/stream_member_list_entry.hbs");
 const render_subscription_settings = require("../templates/subscription_settings.hbs");
diff --git a/static/js/stream_events.js b/static/js/stream_events.js
index c1c6838a07..152d1faad9 100644
--- a/static/js/stream_events.js
+++ b/static/js/stream_events.js
@@ -1,3 +1,5 @@
+"use strict";
+
 // In theory, this function should apply the account-level defaults,
 // however, they are only called after a manual override, so
 // doing so is unnecessary with the current code.  Ideally, we'd do a
diff --git a/static/js/stream_list.js b/static/js/stream_list.js
index f8901a0485..4cbb13410a 100644
--- a/static/js/stream_list.js
+++ b/static/js/stream_list.js
@@ -1,3 +1,5 @@
+"use strict";
+
 const _ = require("lodash");
 
 const render_stream_privacy = require("../templates/stream_privacy.hbs");
diff --git a/static/js/stream_muting.js b/static/js/stream_muting.js
index 9b1ca59d71..6bf1680a8b 100644
--- a/static/js/stream_muting.js
+++ b/static/js/stream_muting.js
@@ -1,3 +1,5 @@
+"use strict";
+
 exports.update_is_muted = function (sub, value) {
     sub.is_muted = value;
 
diff --git a/static/js/stream_popover.js b/static/js/stream_popover.js
index 4b7a2d72c4..90fd7f0eae 100644
--- a/static/js/stream_popover.js
+++ b/static/js/stream_popover.js
@@ -1,3 +1,5 @@
+"use strict";
+
 const render_all_messages_sidebar_actions = require("../templates/all_messages_sidebar_actions.hbs");
 const render_delete_topic_modal = require("../templates/delete_topic_modal.hbs");
 const render_move_topic_to_stream = require("../templates/move_topic_to_stream.hbs");
diff --git a/static/js/stream_sort.js b/static/js/stream_sort.js
index 21b96bc660..2626eac35f 100644
--- a/static/js/stream_sort.js
+++ b/static/js/stream_sort.js
@@ -1,3 +1,5 @@
+"use strict";
+
 const util = require("./util");
 
 let previous_pinned;
diff --git a/static/js/stream_topic_history.js b/static/js/stream_topic_history.js
index 58c3426bd9..9d7ef8eb39 100644
--- a/static/js/stream_topic_history.js
+++ b/static/js/stream_topic_history.js
@@ -1,3 +1,5 @@
+"use strict";
+
 const FoldDict = require("./fold_dict").FoldDict;
 
 const stream_dict = new Map(); // stream_id -> PerStreamHistory object
diff --git a/static/js/stream_ui_updates.js b/static/js/stream_ui_updates.js
index 89aaa6ebf9..5caa9a6b84 100644
--- a/static/js/stream_ui_updates.js
+++ b/static/js/stream_ui_updates.js
@@ -1,3 +1,5 @@
+"use strict";
+
 const render_subscription_count = require("../templates/subscription_count.hbs");
 const render_subscription_setting_icon = require("../templates/subscription_setting_icon.hbs");
 const render_subscription_type = require("../templates/subscription_type.hbs");
diff --git a/static/js/submessage.js b/static/js/submessage.js
index 361b9a6a8d..560ae6fdf4 100644
--- a/static/js/submessage.js
+++ b/static/js/submessage.js
@@ -1,3 +1,5 @@
+"use strict";
+
 exports.get_message_events = function (message) {
     if (message.locally_echoed) {
         return;
diff --git a/static/js/subs.js b/static/js/subs.js
index 07b16750cd..c03b95965f 100644
--- a/static/js/subs.js
+++ b/static/js/subs.js
@@ -1,3 +1,5 @@
+"use strict";
+
 const _ = require("lodash");
 
 const render_subscription = require("../templates/subscription.hbs");
diff --git a/static/js/templates.js b/static/js/templates.js
index 762312de78..b2f1bf6c14 100644
--- a/static/js/templates.js
+++ b/static/js/templates.js
@@ -1,3 +1,5 @@
+"use strict";
+
 const Handlebars = require("handlebars/runtime");
 
 const util = require("./util");
diff --git a/static/js/tictactoe_widget.js b/static/js/tictactoe_widget.js
index 17215fffaa..cdacc3305f 100644
--- a/static/js/tictactoe_widget.js
+++ b/static/js/tictactoe_widget.js
@@ -1,3 +1,5 @@
+"use strict";
+
 const render_widgets_tictactoe_widget = require("../templates/widgets/tictactoe_widget.hbs");
 
 class TicTacToeData {
diff --git a/static/js/timerender.js b/static/js/timerender.js
index fbefc1668b..8f028ec18a 100644
--- a/static/js/timerender.js
+++ b/static/js/timerender.js
@@ -1,3 +1,5 @@
+"use strict";
+
 const moment = require("moment");
 const XDate = require("xdate");
 
diff --git a/static/js/todo_widget.js b/static/js/todo_widget.js
index d149acb36e..50e64ce67e 100644
--- a/static/js/todo_widget.js
+++ b/static/js/todo_widget.js
@@ -1,3 +1,5 @@
+"use strict";
+
 const render_widgets_todo_widget = require("../templates/widgets/todo_widget.hbs");
 const render_widgets_todo_widget_tasks = require("../templates/widgets/todo_widget_tasks.hbs");
 
diff --git a/static/js/top_left_corner.js b/static/js/top_left_corner.js
index be3354ca50..d1182c948e 100644
--- a/static/js/top_left_corner.js
+++ b/static/js/top_left_corner.js
@@ -1,3 +1,5 @@
+"use strict";
+
 exports.update_count_in_dom = function (unread_count_elem, count) {
     const count_span = unread_count_elem.find(".count");
     const value_span = count_span.find(".value");
diff --git a/static/js/topic_generator.js b/static/js/topic_generator.js
index 0685710686..1f67cf3dba 100644
--- a/static/js/topic_generator.js
+++ b/static/js/topic_generator.js
@@ -1,3 +1,5 @@
+"use strict";
+
 exports.sub_list_generator = function (lst, lower, upper) {
     // lower/upper has Python range semantics so if you pass
     // in lower=5 and upper=8, you get elements 5/6/7
diff --git a/static/js/topic_list.js b/static/js/topic_list.js
index ee7b960168..45d9cd6c81 100644
--- a/static/js/topic_list.js
+++ b/static/js/topic_list.js
@@ -1,3 +1,5 @@
+"use strict";
+
 const _ = require("lodash");
 
 const render_more_topics = require("../templates/more_topics.hbs");
diff --git a/static/js/topic_list_data.js b/static/js/topic_list_data.js
index 5d35a3649d..b6ec930ac7 100644
--- a/static/js/topic_list_data.js
+++ b/static/js/topic_list_data.js
@@ -1,3 +1,5 @@
+"use strict";
+
 const max_topics = 5;
 const max_topics_with_unread = 8;
 
diff --git a/static/js/topic_zoom.js b/static/js/topic_zoom.js
index 0f55534aa7..21c879ef08 100644
--- a/static/js/topic_zoom.js
+++ b/static/js/topic_zoom.js
@@ -1,3 +1,5 @@
+"use strict";
+
 let zoomed_in = false;
 
 exports.is_zoomed_in = function () {
diff --git a/static/js/transmit.js b/static/js/transmit.js
index 31cbafceae..5f617d4c3c 100644
--- a/static/js/transmit.js
+++ b/static/js/transmit.js
@@ -1,3 +1,5 @@
+"use strict";
+
 exports.send_message = function (request, on_success, error) {
     channel.post({
         url: "/json/messages",
diff --git a/static/js/tutorial.js b/static/js/tutorial.js
index 53356d7e2f..70fbbf0a02 100644
--- a/static/js/tutorial.js
+++ b/static/js/tutorial.js
@@ -1,3 +1,5 @@
+"use strict";
+
 function set_tutorial_status(status, callback) {
     return channel.post({
         url: "/json/users/me/tutorial_status",
diff --git a/static/js/typeahead_helper.js b/static/js/typeahead_helper.js
index a4019933ea..0d9d0b3304 100644
--- a/static/js/typeahead_helper.js
+++ b/static/js/typeahead_helper.js
@@ -1,3 +1,5 @@
+"use strict";
+
 const Handlebars = require("handlebars/runtime");
 const _ = require("lodash");
 
diff --git a/static/js/typing.js b/static/js/typing.js
index 60f3bb8bf9..6f43dce532 100644
--- a/static/js/typing.js
+++ b/static/js/typing.js
@@ -1,3 +1,5 @@
+"use strict";
+
 const typing_status = require("../shared/js/typing_status");
 
 // This module handles the outbound side of typing indicators.
diff --git a/static/js/typing_data.js b/static/js/typing_data.js
index 2a2017e5bc..73a50a17d0 100644
--- a/static/js/typing_data.js
+++ b/static/js/typing_data.js
@@ -1,3 +1,5 @@
+"use strict";
+
 const _ = require("lodash");
 
 const util = require("./util");
diff --git a/static/js/typing_events.js b/static/js/typing_events.js
index 3f67975dfd..4ce2b98f36 100644
--- a/static/js/typing_events.js
+++ b/static/js/typing_events.js
@@ -1,3 +1,5 @@
+"use strict";
+
 const render_typing_notifications = require("../templates/typing_notifications.hbs");
 
 // See docs/subsystems/typing-indicators.md for details on typing indicators.
diff --git a/static/js/ui.js b/static/js/ui.js
index 3368cbfab5..37b7dce08f 100644
--- a/static/js/ui.js
+++ b/static/js/ui.js
@@ -1,3 +1,5 @@
+"use strict";
+
 const SimpleBar = require("simplebar/dist/simplebar.js");
 
 // What, if anything, obscures the home tab?
diff --git a/static/js/ui_init.js b/static/js/ui_init.js
index 05f5791d23..9e3a0e8cc4 100644
--- a/static/js/ui_init.js
+++ b/static/js/ui_init.js
@@ -1,3 +1,5 @@
+"use strict";
+
 const _ = require("lodash");
 
 const generated_emoji_codes = require("../generated/emoji/emoji_codes.json");
diff --git a/static/js/ui_report.js b/static/js/ui_report.js
index c23491251c..138a884b3e 100644
--- a/static/js/ui_report.js
+++ b/static/js/ui_report.js
@@ -1,3 +1,5 @@
+"use strict";
+
 const _ = require("lodash");
 /* Arguments used in the report_* functions are,
    response- response that we want to display
diff --git a/static/js/ui_util.js b/static/js/ui_util.js
index e063b6ea50..d4fac3283c 100644
--- a/static/js/ui_util.js
+++ b/static/js/ui_util.js
@@ -1,3 +1,5 @@
+"use strict";
+
 // Add functions to this that have no non-trivial
 // dependencies other than jQuery.
 
diff --git a/static/js/unread.js b/static/js/unread.js
index 4a8ad4fbae..6744226fb0 100644
--- a/static/js/unread.js
+++ b/static/js/unread.js
@@ -1,3 +1,5 @@
+"use strict";
+
 const FoldDict = require("./fold_dict").FoldDict;
 const util = require("./util");
 
diff --git a/static/js/unread_ops.js b/static/js/unread_ops.js
index d2e7d116fc..a8d8245f1e 100644
--- a/static/js/unread_ops.js
+++ b/static/js/unread_ops.js
@@ -1,3 +1,5 @@
+"use strict";
+
 exports.mark_all_as_read = function () {
     unread.declare_bankruptcy();
     unread_ui.update_unread_counts();
diff --git a/static/js/unread_ui.js b/static/js/unread_ui.js
index cbe8388f3e..b7a3625e8b 100644
--- a/static/js/unread_ui.js
+++ b/static/js/unread_ui.js
@@ -1,3 +1,5 @@
+"use strict";
+
 const XDate = require("xdate");
 
 let last_mention_count = 0;
diff --git a/static/js/upload.js b/static/js/upload.js
index e97f98c6e8..2f26e180c0 100644
--- a/static/js/upload.js
+++ b/static/js/upload.js
@@ -1,3 +1,5 @@
+"use strict";
+
 const Uppy = require("@uppy/core");
 const ProgressBar = require("@uppy/progress-bar");
 const XHRUpload = require("@uppy/xhr-upload");
diff --git a/static/js/upload_widget.js b/static/js/upload_widget.js
index a58cb50a2a..cc97df2239 100644
--- a/static/js/upload_widget.js
+++ b/static/js/upload_widget.js
@@ -1,3 +1,5 @@
+"use strict";
+
 const default_max_file_size = 5;
 
 const supported_types = ["image/jpeg", "image/png", "image/gif", "image/tiff"];
diff --git a/static/js/user_events.js b/static/js/user_events.js
index ff5b7e8620..11d4a053d3 100644
--- a/static/js/user_events.js
+++ b/static/js/user_events.js
@@ -1,3 +1,5 @@
+"use strict";
+
 // This module is kind of small, but it will help us keep
 // server_events.js simple while breaking some circular
 // dependencies that existed when this code was in people.js.
diff --git a/static/js/user_groups.js b/static/js/user_groups.js
index 1f899f4186..3eb1cda348 100644
--- a/static/js/user_groups.js
+++ b/static/js/user_groups.js
@@ -1,3 +1,5 @@
+"use strict";
+
 const FoldDict = require("./fold_dict").FoldDict;
 
 let user_group_name_dict;
diff --git a/static/js/user_pill.js b/static/js/user_pill.js
index c5fb6c99ab..721959bd47 100644
--- a/static/js/user_pill.js
+++ b/static/js/user_pill.js
@@ -1,3 +1,5 @@
+"use strict";
+
 // This will be used for pills for things like composing PMs
 // or adding users to a stream/group.
 const settings_data = require("./settings_data");
diff --git a/static/js/user_search.js b/static/js/user_search.js
index 125d09858f..6f3acf8f2c 100644
--- a/static/js/user_search.js
+++ b/static/js/user_search.js
@@ -1,3 +1,5 @@
+"use strict";
+
 class UserSearch {
     // This is mostly view code to manage the user search widget
     // above the buddy list.  We rely on other code to manage the
diff --git a/static/js/user_status.js b/static/js/user_status.js
index 930d71f7d0..df35ab0ed3 100644
--- a/static/js/user_status.js
+++ b/static/js/user_status.js
@@ -1,3 +1,5 @@
+"use strict";
+
 const away_user_ids = new Set();
 const user_info = new Map();
 
diff --git a/static/js/user_status_ui.js b/static/js/user_status_ui.js
index d977619d4c..c6641622fb 100644
--- a/static/js/user_status_ui.js
+++ b/static/js/user_status_ui.js
@@ -1,3 +1,5 @@
+"use strict";
+
 exports.input_field = function () {
     return $(".user_status_overlay input.user_status");
 };
diff --git a/static/js/util.js b/static/js/util.js
index 9261b51d01..7d09cbe779 100644
--- a/static/js/util.js
+++ b/static/js/util.js
@@ -1,3 +1,5 @@
+"use strict";
+
 const _ = require("lodash");
 // From MDN: https://developer.mozilla.org/en-US/docs/JavaScript/Reference/Global_Objects/Math/random
 exports.random_int = function random_int(min, max) {
diff --git a/static/js/vdom.js b/static/js/vdom.js
index 8b46c83a66..555ce41196 100644
--- a/static/js/vdom.js
+++ b/static/js/vdom.js
@@ -1,3 +1,5 @@
+"use strict";
+
 const _ = require("lodash");
 
 exports.eq_array = (a, b, eq) => {
diff --git a/static/js/widgetize.js b/static/js/widgetize.js
index 5ff0346fdd..7d4cde6b9a 100644
--- a/static/js/widgetize.js
+++ b/static/js/widgetize.js
@@ -1,3 +1,5 @@
+"use strict";
+
 const widgets = new Map([
     ["poll", poll_widget],
     ["tictactoe", tictactoe_widget],
diff --git a/static/js/zcommand.js b/static/js/zcommand.js
index f50d47eea3..4223043c36 100644
--- a/static/js/zcommand.js
+++ b/static/js/zcommand.js
@@ -1,3 +1,5 @@
+"use strict";
+
 const marked = require("../third/marked/lib/marked");
 
 /*
diff --git a/static/js/zform.js b/static/js/zform.js
index 89d6cc8b82..50f5ab0499 100644
--- a/static/js/zform.js
+++ b/static/js/zform.js
@@ -1,3 +1,5 @@
+"use strict";
+
 const render_widgets_zform_choices = require("../templates/widgets/zform_choices.hbs");
 
 exports.validate_extra_data = function (data) {
diff --git a/static/js/zulip.js b/static/js/zulip.js
index 30632fa5ab..ec7189965d 100644
--- a/static/js/zulip.js
+++ b/static/js/zulip.js
@@ -1,3 +1,5 @@
+"use strict";
+
 // This file is being eliminated as part of the general purge of
 // global variables from Zulip (everything is being moved into
 // modules).  Please don't add things here.
diff --git a/tools/check-openapi b/tools/check-openapi
index 4aa4e88654..0f04f7ef53 100755
--- a/tools/check-openapi
+++ b/tools/check-openapi
@@ -1,4 +1,5 @@
 #!/usr/bin/env node
+"use strict";
 
 const fs = require("fs");
 
diff --git a/tools/debug-require.js b/tools/debug-require.js
index 2aa998e143..60becbd372 100644
--- a/tools/debug-require.js
+++ b/tools/debug-require.js
@@ -1,3 +1,5 @@
+"use strict";
+
 /* global __webpack_require__ */
 
 var webpackModules;
diff --git a/tools/message-screenshot.js b/tools/message-screenshot.js
index 2f098bc7f0..63fba2dd6b 100644
--- a/tools/message-screenshot.js
+++ b/tools/message-screenshot.js
@@ -1,3 +1,5 @@
+"use strict";
+
 const path = require("path");
 
 const commander = require("commander");
diff --git a/tools/node_lib/dump_fixtures.js b/tools/node_lib/dump_fixtures.js
index a31538a7b5..69329a2d87 100644
--- a/tools/node_lib/dump_fixtures.js
+++ b/tools/node_lib/dump_fixtures.js
@@ -1,3 +1,5 @@
+"use strict";
+
 const events = require("../../frontend_tests/node_tests/lib/events.js");
 
 console.info(JSON.stringify(events.fixtures, null, 4));
diff --git a/zerver/openapi/javascript_examples.js b/zerver/openapi/javascript_examples.js
index faf1106c85..7ff6c1412a 100644
--- a/zerver/openapi/javascript_examples.js
+++ b/zerver/openapi/javascript_examples.js
@@ -1,3 +1,5 @@
+"use strict";
+
 /* eslint-disable arrow-body-style */
 /*
   This file makes use of functional comments in a way that makes the