From 719546641f2b3ad556baae03f508a718811ade8f Mon Sep 17 00:00:00 2001
From: Anders Kaseorg <anders@zulipchat.com>
Date: Fri, 7 Feb 2020 19:55:06 -0800
Subject: [PATCH] =?UTF-8?q?js:=20Convert=20a.indexOf(=E2=80=A6)=20!=3D=3D?=
 =?UTF-8?q?=20-1=20to=20a.includes(=E2=80=A6).?=
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

Babel polyfills this for us for Internet Explorer.

import * as babelParser from "recast/parsers/babel";
import * as recast from "recast";
import * as tsParser from "recast/parsers/typescript";
import { builders as b, namedTypes as n } from "ast-types";
import K from "ast-types/gen/kinds";
import fs from "fs";
import path from "path";
import process from "process";

const checkExpression = (node: n.Node): node is K.ExpressionKind =>
  n.Expression.check(node);

for (const file of process.argv.slice(2)) {
  console.log("Parsing", file);
  const ast = recast.parse(fs.readFileSync(file, { encoding: "utf8" }), {
    parser: path.extname(file) === ".ts" ? tsParser : babelParser,
  });
  let changed = false;

  recast.visit(ast, {
    visitBinaryExpression(path) {
      const { operator, left, right } = path.node;
      if (
        n.CallExpression.check(left) &&
        n.MemberExpression.check(left.callee) &&
        !left.callee.computed &&
        n.Identifier.check(left.callee.property) &&
        left.callee.property.name === "indexOf" &&
        left.arguments.length === 1 &&
        checkExpression(left.arguments[0]) &&
        ((["===", "!==", "==", "!=", ">", "<="].includes(operator) &&
          n.UnaryExpression.check(right) &&
          right.operator == "-" &&
          n.Literal.check(right.argument) &&
          right.argument.value === 1) ||
          ([">=", "<"].includes(operator) &&
            n.Literal.check(right) &&
            right.value === 0))
      ) {
        const test = b.callExpression(
          b.memberExpression(left.callee.object, b.identifier("includes")),
          [left.arguments[0]]
        );
        path.replace(
          ["!==", "!=", ">", ">="].includes(operator)
            ? test
            : b.unaryExpression("!", test)
        );
        changed = true;
      }
      this.traverse(path);
    },
  });

  if (changed) {
    console.log("Writing", file);
    fs.writeFileSync(file, recast.print(ast).code, { encoding: "utf8" });
  }
}

Signed-off-by: Anders Kaseorg <anders@zulipchat.com>
---
 docs/subsystems/input-pills.md                       |  2 +-
 frontend_tests/node_tests/markdown.js                | 10 +++++-----
 frontend_tests/node_tests/people_errors.js           |  2 +-
 frontend_tests/node_tests/search_suggestion.js       |  2 +-
 .../node_tests/search_suggestion_legacy.js           |  2 +-
 frontend_tests/node_tests/stream_data.js             |  6 +++---
 frontend_tests/node_tests/templates.js               |  4 ++--
 frontend_tests/zjsunit/finder.js                     |  2 +-
 frontend_tests/zjsunit/zblueslip.js                  |  4 ++--
 frontend_tests/zjsunit/zjquery.js                    | 10 +++++-----
 static/js/activity.js                                |  2 +-
 static/js/alert_words_ui.js                          |  2 +-
 static/js/attachments_ui.js                          |  2 +-
 static/js/common.js                                  |  2 +-
 static/js/compose.js                                 |  2 +-
 static/js/composebox_typeahead.js                    |  8 ++++----
 static/js/emoji.js                                   |  8 ++++----
 static/js/emoji_picker.js                            |  2 +-
 static/js/filter.js                                  |  6 +++---
 static/js/hashchange.js                              |  2 +-
 static/js/hotkey.js                                  |  2 +-
 static/js/markdown.js                                |  2 +-
 static/js/message_events.js                          |  4 ++--
 static/js/message_fetch.js                           |  4 ++--
 static/js/message_flags.js                           |  2 +-
 static/js/message_store.js                           |  4 ++--
 static/js/narrow.js                                  |  8 ++++----
 static/js/notifications.js                           |  9 ++++++---
 static/js/people.js                                  |  6 ++----
 static/js/pm_list.js                                 |  2 +-
 static/js/portico/integrations.js                    |  2 +-
 static/js/portico/landing-page.js                    |  6 +++---
 static/js/portico/tabbed-instructions.js             |  4 ++--
 static/js/reactions.js                               |  2 +-
 static/js/rtl.js                                     |  4 ++--
 static/js/search_suggestion.js                       |  6 +++---
 static/js/search_util.js                             |  2 +-
 static/js/settings_display.js                        |  2 +-
 static/js/settings_emoji.js                          |  2 +-
 static/js/settings_exports.js                        |  2 +-
 static/js/settings_invites.js                        |  4 ++--
 static/js/settings_linkifiers.js                     |  6 ++----
 static/js/settings_org.js                            |  6 +++---
 static/js/settings_streams.js                        |  2 +-
 static/js/settings_users.js                          |  6 ++----
 static/js/stream_create.js                           |  6 +++---
 static/js/stream_edit.js                             | 12 ++++++------
 static/js/ui.js                                      |  2 +-
 static/js/upload_widget.js                           |  2 +-
 static/js/user_pill.js                               | 10 +++++-----
 static/js/util.js                                    |  2 +-
 static/js/zcommand.js                                |  4 ++--
 static/shared/js/typeahead.js                        |  2 +-
 tools/check-openapi                                  |  2 +-
 tools/linter_lib/custom_check.py                     |  3 ---
 55 files changed, 109 insertions(+), 115 deletions(-)

diff --git a/docs/subsystems/input-pills.md b/docs/subsystems/input-pills.md
index edf3e0feac..be9c870cba 100644
--- a/docs/subsystems/input-pills.md
+++ b/docs/subsystems/input-pills.md
@@ -57,7 +57,7 @@ exports.typeahead_source = function (pill_widget) {
 exports.filter_taken_users = function (items, pill_widget) {
     const taken_user_ids = exports.get_user_ids(pill_widget);
     items = _.filter(items, function (item) {
-        return taken_user_ids.indexOf(item.user_id) === -1;
+        return !taken_user_ids.includes(item.user_id);
     });
     return items;
 };
diff --git a/frontend_tests/node_tests/markdown.js b/frontend_tests/node_tests/markdown.js
index e27a5eac59..44a8c27ae8 100644
--- a/frontend_tests/node_tests/markdown.js
+++ b/frontend_tests/node_tests/markdown.js
@@ -432,8 +432,8 @@ run_test('topic_links', () => {
     message = {type: 'stream', topic: "New ZBUG_123 with #456 link here"};
     markdown.add_topic_links(message);
     assert.equal(util.get_topic_links(message).length, 2);
-    assert(util.get_topic_links(message).indexOf("https://trac2.zulip.net/ticket/123") !== -1);
-    assert(util.get_topic_links(message).indexOf("https://trac.zulip.net/ticket/456") !== -1);
+    assert(util.get_topic_links(message).includes("https://trac2.zulip.net/ticket/123"));
+    assert(util.get_topic_links(message).includes("https://trac.zulip.net/ticket/456"));
 
     message = {type: 'stream', topic: "One ZGROUP_123:45 link here"};
     markdown.add_topic_links(message);
@@ -448,9 +448,9 @@ run_test('topic_links', () => {
     message = {type: 'stream', topic: "#456 https://google.com https://github.com"};
     markdown.add_topic_links(message);
     assert.equal(util.get_topic_links(message).length, 3);
-    assert(util.get_topic_links(message).indexOf("https://google.com") !== -1);
-    assert(util.get_topic_links(message).indexOf("https://github.com") !== -1);
-    assert(util.get_topic_links(message).indexOf("https://trac.zulip.net/ticket/456") !== -1);
+    assert(util.get_topic_links(message).includes("https://google.com"));
+    assert(util.get_topic_links(message).includes("https://github.com"));
+    assert(util.get_topic_links(message).includes("https://trac.zulip.net/ticket/456"));
 
     message = {type: "not-stream"};
     markdown.add_topic_links(message);
diff --git a/frontend_tests/node_tests/people_errors.js b/frontend_tests/node_tests/people_errors.js
index 71dd4ee666..06ccf23f6a 100644
--- a/frontend_tests/node_tests/people_errors.js
+++ b/frontend_tests/node_tests/people_errors.js
@@ -121,7 +121,7 @@ run_test('blueslip', () => {
     };
     blueslip.set_test_data('error', 'Unknown user id in message: 42');
     const reply_to = people.pm_reply_to(message);
-    assert(reply_to.indexOf('?') > -1);
+    assert(reply_to.includes('?'));
     assert.equal(blueslip.get_test_logs('error').length, 1);
     blueslip.clear_test_data();
 
diff --git a/frontend_tests/node_tests/search_suggestion.js b/frontend_tests/node_tests/search_suggestion.js
index 156808a556..a2b103147e 100644
--- a/frontend_tests/node_tests/search_suggestion.js
+++ b/frontend_tests/node_tests/search_suggestion.js
@@ -714,7 +714,7 @@ run_test('sent_by_me_suggestions', () => {
 
     let query = '';
     let suggestions = get_suggestions('', query);
-    assert(suggestions.strings.indexOf('sender:bob@zulip.com') !== -1);
+    assert(suggestions.strings.includes('sender:bob@zulip.com'));
     assert.equal(suggestions.lookup_table['sender:bob@zulip.com'].description,
                  'Sent by me');
 
diff --git a/frontend_tests/node_tests/search_suggestion_legacy.js b/frontend_tests/node_tests/search_suggestion_legacy.js
index d4d4520c69..7ff98c99da 100644
--- a/frontend_tests/node_tests/search_suggestion_legacy.js
+++ b/frontend_tests/node_tests/search_suggestion_legacy.js
@@ -683,7 +683,7 @@ run_test('sent_by_me_suggestions', () => {
 
     let query = '';
     let suggestions = search.get_suggestions_legacy(query);
-    assert(suggestions.strings.indexOf('sender:bob@zulip.com') !== -1);
+    assert(suggestions.strings.includes('sender:bob@zulip.com'));
     assert.equal(suggestions.lookup_table['sender:bob@zulip.com'].description,
                  'Sent by me');
 
diff --git a/frontend_tests/node_tests/stream_data.js b/frontend_tests/node_tests/stream_data.js
index 1aea469714..a92f3d2258 100644
--- a/frontend_tests/node_tests/stream_data.js
+++ b/frontend_tests/node_tests/stream_data.js
@@ -797,9 +797,9 @@ run_test('initialize', () => {
     assert(!stream_data.is_filtering_inactives());
 
     const stream_names = stream_data.get_streams_for_admin().map(elem => elem.name);
-    assert(stream_names.indexOf('subscriptions') !== -1);
-    assert(stream_names.indexOf('unsubscribed') !== -1);
-    assert(stream_names.indexOf('never_subscribed') !== -1);
+    assert(stream_names.includes('subscriptions'));
+    assert(stream_names.includes('unsubscribed'));
+    assert(stream_names.includes('never_subscribed'));
     assert(!page_params.subscriptions);
     assert(!page_params.unsubscribed);
     assert(!page_params.never_subscribed);
diff --git a/frontend_tests/node_tests/templates.js b/frontend_tests/node_tests/templates.js
index 93e11bb8b8..8340953763 100644
--- a/frontend_tests/node_tests/templates.js
+++ b/frontend_tests/node_tests/templates.js
@@ -1754,8 +1754,8 @@ run_test('recipient_row', () => {
         ],
     };
     const html = render('recipient_row', data);
-    assert(html.indexOf('<script>alert("Hello")</script>') === -1);
-    assert(html.indexOf('&lt;script&gt;alert(&quot;Hello&quot;)&lt;/script&gt;') !== -1);
+    assert(!html.includes('<script>alert("Hello")</script>'));
+    assert(html.includes('&lt;script&gt;alert(&quot;Hello&quot;)&lt;/script&gt;'));
 });
 
 run_test('invitation_failed_error', () => {
diff --git a/frontend_tests/zjsunit/finder.js b/frontend_tests/zjsunit/finder.js
index c604961161..366d1d57dd 100644
--- a/frontend_tests/zjsunit/finder.js
+++ b/frontend_tests/zjsunit/finder.js
@@ -23,7 +23,7 @@ exports.find_files_to_run = function () {
 
     if (oneFileFilter.length > 0) {
         tests = tests.filter(function (filename) {
-            return oneFileFilter.indexOf(filename) !== -1;
+            return oneFileFilter.includes(filename);
         });
         testsDifference = _.difference(oneFileFilter, tests);
     }
diff --git a/frontend_tests/zjsunit/zblueslip.js b/frontend_tests/zjsunit/zblueslip.js
index 1bbecf01d5..a8ab8bd8d9 100644
--- a/frontend_tests/zjsunit/zblueslip.js
+++ b/frontend_tests/zjsunit/zblueslip.js
@@ -63,8 +63,8 @@ exports.make_zblueslip = function () {
         }
         lib[name] = function (message, more_info, stack) {
             lib.test_logs[name].push({message, more_info, stack});
-            const exact_match_fail = lib.test_data[name].indexOf(message) === -1;
-            const string_match_fail = lib.test_data[name].indexOf(message.toString()) === -1;
+            const exact_match_fail = !lib.test_data[name].includes(message);
+            const string_match_fail = !lib.test_data[name].includes(message.toString());
             if (exact_match_fail && string_match_fail) {
                 const error = Error(`Invalid ${name} message: "${message}".`);
                 error.blueslip = true;
diff --git a/frontend_tests/zjsunit/zjquery.js b/frontend_tests/zjsunit/zjquery.js
index 66f1b55766..0095ee83f4 100644
--- a/frontend_tests/zjsunit/zjquery.js
+++ b/frontend_tests/zjsunit/zjquery.js
@@ -168,7 +168,7 @@ exports.make_new_elem = function (selector, opts) {
         closest: function (selector) {
             const elem = self;
             const search = selector.startsWith('.') || selector.startsWith('#') ? selector.substring(1) : selector;
-            if (elem.selector.indexOf(search) > -1) {
+            if (elem.selector.includes(search)) {
                 return elem;
             } else if (parents_result.get(selector)) {
                 return parents_result.get(selector);
@@ -486,15 +486,15 @@ exports.make_zjquery = function (opts) {
         }
 
         const valid_selector =
-            '<#.'.indexOf(selector[0]) >= 0 ||
+            '<#.'.includes(selector[0]) ||
             selector === 'window-stub' ||
             selector === 'document-stub' ||
             selector === 'body' ||
             selector === 'html' ||
             selector.location ||
-            selector.indexOf('#') >= 0 ||
-            selector.indexOf('.') >= 0 ||
-            selector.indexOf('[') >= 0 && selector.indexOf(']') >= selector.indexOf('[');
+            selector.includes('#') ||
+            selector.includes('.') ||
+            selector.includes('[') && selector.indexOf(']') >= selector.indexOf('[');
 
         assert(valid_selector,
                'Invalid selector: ' + selector +
diff --git a/static/js/activity.js b/static/js/activity.js
index c690fcfcd8..ffb93ecc88 100644
--- a/static/js/activity.js
+++ b/static/js/activity.js
@@ -87,7 +87,7 @@ exports.update_dom_with_unread_counts = function (counts) {
 
     for (const [user_ids_string, count] of counts.pm_count) {
         // TODO: just use user_ids_string in our markup
-        const is_pm = user_ids_string.indexOf(',') < 0;
+        const is_pm = !user_ids_string.includes(',');
         if (is_pm) {
             set_pm_count(user_ids_string, count);
         } else {
diff --git a/static/js/alert_words_ui.js b/static/js/alert_words_ui.js
index c74fca822a..ec9933c7d4 100644
--- a/static/js/alert_words_ui.js
+++ b/static/js/alert_words_ui.js
@@ -40,7 +40,7 @@ function add_alert_word(alert_word) {
     if (alert_word === '') {
         update_alert_word_status(i18n.t("Alert word can't be empty!"), true);
         return;
-    } else if (alert_words.words.indexOf(alert_word) !== -1) {
+    } else if (alert_words.words.includes(alert_word)) {
         update_alert_word_status(i18n.t("Alert word already exists!"), true);
         return;
     }
diff --git a/static/js/attachments_ui.js b/static/js/attachments_ui.js
index a87ca4f672..87a1b4f281 100644
--- a/static/js/attachments_ui.js
+++ b/static/js/attachments_ui.js
@@ -69,7 +69,7 @@ function render_attachments_ui() {
         filter: {
             element: $search_input,
             predicate: function (item, value) {
-                return item.name.toLocaleLowerCase().indexOf(value) >= 0;
+                return item.name.toLocaleLowerCase().includes(value);
             },
             onupdate: function () {
                 ui.reset_scrollbar(uploaded_files_table.closest(".progressive-table-wrapper"));
diff --git a/static/js/common.js b/static/js/common.js
index b655213454..cb8b4056a8 100644
--- a/static/js/common.js
+++ b/static/js/common.js
@@ -119,7 +119,7 @@ exports.adjust_mac_shortcuts = function (key_elem_class, require_cmd_style) {
         let key_text = $(this).text();
         const keys = key_text.match(/[^\s\+]+/g);
 
-        if (key_text.indexOf('Ctrl') > -1 && require_cmd_style) {
+        if (key_text.includes('Ctrl') && require_cmd_style) {
             $(this).addClass("mac-cmd-key");
         }
 
diff --git a/static/js/compose.js b/static/js/compose.js
index 900ab4da2e..4b9c99cdff 100644
--- a/static/js/compose.js
+++ b/static/js/compose.js
@@ -891,7 +891,7 @@ exports.warn_if_mentioning_unsubscribed_user = function (mentioned) {
             return $(user_row).data('useremail');
         });
 
-        if (existing_invites.indexOf(email) === -1) {
+        if (!existing_invites.includes(email)) {
             const context = {
                 email: email,
                 name: mentioned.full_name,
diff --git a/static/js/composebox_typeahead.js b/static/js/composebox_typeahead.js
index e3a6220871..17997885e9 100644
--- a/static/js/composebox_typeahead.js
+++ b/static/js/composebox_typeahead.js
@@ -50,7 +50,7 @@ exports.topics_seen_for = function (stream_name) {
 function get_language_matcher(query) {
     query = query.toLowerCase();
     return function (lang) {
-        return lang.indexOf(query) !== -1;
+        return lang.includes(query);
     };
 }
 
@@ -557,7 +557,7 @@ exports.get_candidates = function (query) {
 
     // We will likely want to extend this list to be more i18n-friendly.
     const terminal_symbols = ',.;?!()[] "\'\n\t';
-    if (rest !== '' && terminal_symbols.indexOf(rest[0]) === -1) {
+    if (rest !== '' && !terminal_symbols.includes(rest[0])) {
         return false;
     }
 
@@ -974,7 +974,7 @@ exports.initialize = function () {
         },
         sorter: function (items) {
             const sorted = typeahead_helper.sorter(this.query, items, function (x) {return x;});
-            if (sorted.length > 0 && sorted.indexOf(this.query) === -1) {
+            if (sorted.length > 0 && !sorted.includes(this.query)) {
                 sorted.unshift(this.query);
             }
             return sorted;
@@ -1002,7 +1002,7 @@ exports.initialize = function () {
                     // filter out inserted users and current user from pill insertion
                     const inserted_users = user_pill.get_user_ids(compose_pm_pill.widget);
                     const current_user = people.is_current_user(user.email);
-                    if (inserted_users.indexOf(user.user_id) === -1 && !current_user) {
+                    if (!inserted_users.includes(user.user_id) && !current_user) {
                         compose_pm_pill.set_from_typeahead(user);
                     }
                 }
diff --git a/static/js/emoji.js b/static/js/emoji.js
index cbe0d05c5f..04b1264db5 100644
--- a/static/js/emoji.js
+++ b/static/js/emoji.js
@@ -152,10 +152,10 @@ exports.translate_emoticons_to_names = function translate_emoticons_to_names(tex
         const prev_char = str[offset - 1];
         const next_char = str[offset + match.length];
 
-        const symbol_at_start = terminal_symbols.indexOf(prev_char) !== -1;
-        const symbol_at_end = terminal_symbols.indexOf(next_char) !== -1;
-        const non_space_at_start = symbols_except_space.indexOf(prev_char) !== -1;
-        const non_space_at_end = symbols_except_space.indexOf(next_char) !== -1;
+        const symbol_at_start = terminal_symbols.includes(prev_char);
+        const symbol_at_end = terminal_symbols.includes(next_char);
+        const non_space_at_start = symbols_except_space.includes(prev_char);
+        const non_space_at_end = symbols_except_space.includes(next_char);
         const valid_start = symbol_at_start || offset === 0;
         const valid_end = symbol_at_end || offset === str.length - match.length;
 
diff --git a/static/js/emoji_picker.js b/static/js/emoji_picker.js
index ffdea9a90a..4414e21ace 100644
--- a/static/js/emoji_picker.js
+++ b/static/js/emoji_picker.js
@@ -218,7 +218,7 @@ function filter_emojis() {
             for (const emoji_dict of emojis) {
                 for (const alias of emoji_dict.aliases) {
                     const match = _.every(search_terms, function (search_term) {
-                        return alias.indexOf(search_term) >= 0;
+                        return alias.includes(search_term);
                     });
                     if (match) {
                         search_results.push(_.extend({}, emoji_dict, {name: alias}));
diff --git a/static/js/filter.js b/static/js/filter.js
index 2822c2dec7..fdd1a876fa 100644
--- a/static/js/filter.js
+++ b/static/js/filter.js
@@ -121,7 +121,7 @@ function message_matches_search_term(message, operator, operand) {
         if (!user_ids) {
             return false;
         }
-        return user_ids.indexOf(operand_ids[0]) !== -1;
+        return user_ids.includes(operand_ids[0]);
         // We should also check if the current user is in the recipient list (user_ids) of the
         // message, but it is implicit by the fact that the current user has access to the message.
     }
@@ -682,7 +682,7 @@ function describe_is_operator(operator) {
     const verb = operator.negated ? 'exclude ' : '';
     const operand = operator.operand;
     const operand_list = ['private', 'starred', 'alerted', 'unread'];
-    if (operand_list.indexOf(operand) !== -1) {
+    if (operand_list.includes(operand)) {
         return verb + operand + ' messages';
     } else if (operand === 'mentioned') {
         return verb + '@-mentions';
@@ -722,7 +722,7 @@ function describe_unescaped(operators) {
             // search_suggestion.get_suggestions takes care that this message will
             // only be shown if the `has` operator is not at the last.
             const valid_has_operands = ['image', 'images', 'link', 'links', 'attachment', 'attachments'];
-            if (valid_has_operands.indexOf(operand) === -1) {
+            if (!valid_has_operands.includes(operand)) {
                 return 'invalid ' + operand + ' operand for has operator';
             }
         }
diff --git a/static/js/hashchange.js b/static/js/hashchange.js
index b1403bafa0..fa4b507194 100644
--- a/static/js/hashchange.js
+++ b/static/js/hashchange.js
@@ -66,7 +66,7 @@ function is_overlay_hash(hash) {
     const overlay_list = ["streams", "drafts", "settings", "organization", "invite"];
     const main_hash = hash_util.get_hash_category(hash);
 
-    return overlay_list.indexOf(main_hash) > -1;
+    return overlay_list.includes(main_hash);
 }
 
 // Returns true if this function performed a narrow
diff --git a/static/js/hotkey.js b/static/js/hotkey.js
index 2e71c5cbb8..201322f488 100644
--- a/static/js/hotkey.js
+++ b/static/js/hotkey.js
@@ -535,7 +535,7 @@ exports.process_hotkey = function (e, hotkey) {
         }
     }
 
-    if (menu_dropdown_hotkeys.indexOf(event_name) !== -1) {
+    if (menu_dropdown_hotkeys.includes(event_name)) {
         if (popovers.actions_popped()) {
             popovers.actions_menu_handle_keyboard(event_name);
             return true;
diff --git a/static/js/markdown.js b/static/js/markdown.js
index d2052ba560..a2dd55c976 100644
--- a/static/js/markdown.js
+++ b/static/js/markdown.js
@@ -285,7 +285,7 @@ function python_to_js_filter(pattern, url) {
         const py_flags = match[1].split("");
 
         for (const flag of py_flags) {
-            if ("im".indexOf(flag) !== -1) {
+            if ("im".includes(flag)) {
                 js_flags += flag;
             }
         }
diff --git a/static/js/message_events.js b/static/js/message_events.js
index a14b68c5de..caf6811cb5 100644
--- a/static/js/message_events.js
+++ b/static/js/message_events.js
@@ -142,7 +142,7 @@ exports.update_messages = function update_messages(events) {
             // where the user initiated the edit.
             topic_edited = true;
 
-            const going_forward_change = ['change_later', 'change_all'].indexOf(event.propagate_mode) >= 0;
+            const going_forward_change = ['change_later', 'change_all'].includes(event.propagate_mode);
 
             const stream_name = stream_data.get_sub_by_id(event.stream_id).name;
             const compose_stream_name = compose_state.stream_name();
@@ -161,7 +161,7 @@ exports.update_messages = function update_messages(events) {
             const current_filter = narrow_state.filter();
             if (going_forward_change) {
                 const current_id = current_msg_list.selected_id();
-                const selection_changed_topic = event.message_ids.indexOf(current_id) >= 0;
+                const selection_changed_topic = event.message_ids.includes(current_id);
                 if (selection_changed_topic) {
                     if (current_filter && stream_name) {
                         if (current_filter.has_topic(stream_name, orig_topic)) {
diff --git a/static/js/message_fetch.js b/static/js/message_fetch.js
index f5103674df..0e5dde2009 100644
--- a/static/js/message_fetch.js
+++ b/static/js/message_fetch.js
@@ -119,11 +119,11 @@ function handle_operators_supporting_id_based_api(data) {
 
     data.narrow = JSON.parse(data.narrow);
     data.narrow = _.map(data.narrow, function (filter) {
-        if (operators_supporting_ids.indexOf(filter.operator) !== -1) {
+        if (operators_supporting_ids.includes(filter.operator)) {
             filter.operand = people.emails_strings_to_user_ids_array(filter.operand);
         }
 
-        if (operators_supporting_id.indexOf(filter.operator) !== -1) {
+        if (operators_supporting_id.includes(filter.operator)) {
             if (filter.operator === 'stream') {
                 const stream_id = stream_data.get_stream_id(filter.operand);
                 if (stream_id !== undefined) {
diff --git a/static/js/message_flags.js b/static/js/message_flags.js
index 3a021fc1a3..e1b5207e72 100644
--- a/static/js/message_flags.js
+++ b/static/js/message_flags.js
@@ -51,7 +51,7 @@ exports.send_read = (function () {
         }
 
         queue = _.filter(queue, function (message) {
-            return data.messages.indexOf(message.id) === -1;
+            return !data.messages.includes(message.id);
         });
 
         if (queue.length > 0) {
diff --git a/static/js/message_store.js b/static/js/message_store.js
index 7417fc650e..8d1476f33b 100644
--- a/static/js/message_store.js
+++ b/static/js/message_store.js
@@ -78,7 +78,7 @@ exports.set_message_booleans = function (message) {
     const flags = message.flags || [];
 
     function convert_flag(flag_name) {
-        return flags.indexOf(flag_name) >= 0;
+        return flags.includes(flag_name);
     }
 
     message.unread = !convert_flag('read');
@@ -115,7 +115,7 @@ exports.update_booleans = function (message, flags) {
     // we are vulnerable to race conditions, so only update flags
     // that are driven by message content.
     function convert_flag(flag_name) {
-        return flags.indexOf(flag_name) >= 0;
+        return flags.includes(flag_name);
     }
 
     message.mentioned = convert_flag('mentioned') || convert_flag('wildcard_mentioned');
diff --git a/static/js/narrow.js b/static/js/narrow.js
index ed2110c4d5..46724cad79 100644
--- a/static/js/narrow.js
+++ b/static/js/narrow.js
@@ -83,7 +83,7 @@ function update_narrow_title(filter) {
                 exports.narrow_title = names + " and others";
             }
         } else {
-            if (emails.indexOf(',') > -1) {
+            if (emails.includes(',')) {
                 exports.narrow_title = "Invalid users";
             } else {
                 exports.narrow_title = "Invalid user";
@@ -725,7 +725,7 @@ exports.to_compose_target = function () {
         const topics = topic_data.get_recent_names(stream_id);
         const operators = [{operator: 'stream', operand: stream_name}];
         const topic = compose_state.topic();
-        if (topics.indexOf(topic) !== -1) {
+        if (topics.includes(topic)) {
             operators.push({operator: 'topic', operand: topic});
         }
         exports.activate(operators, opts);
@@ -978,12 +978,12 @@ function pick_empty_narrow_banner() {
         return $("#empty_search_narrow_message");
     } else if (first_operator === "pm-with") {
         if (!people.is_valid_bulk_emails_for_compose(first_operand.split(','))) {
-            if (first_operand.indexOf(',') === -1) {
+            if (!first_operand.includes(',')) {
                 return $("#non_existing_user");
             }
             return $("#non_existing_users");
         }
-        if (first_operand.indexOf(',') === -1) {
+        if (!first_operand.includes(',')) {
             // You have no private messages with this person
             if (people.is_current_user(first_operand)) {
                 return $("#empty_narrow_self_private_message");
diff --git a/static/js/notifications.js b/static/js/notifications.js
index c4187dc13e..a7bffa30cc 100644
--- a/static/js/notifications.js
+++ b/static/js/notifications.js
@@ -753,12 +753,15 @@ exports.handle_global_notification_updates = function (notification_name, settin
     // Update the global settings checked when determining if we should notify
     // for a given message. These settings do not affect whether or not a
     // particular stream should receive notifications.
-    if (settings_notifications.all_notification_settings_labels.indexOf(notification_name) !== -1) {
+    if (settings_notifications.all_notification_settings_labels.includes(notification_name)) {
         page_params[notification_name] = setting;
     }
 
-    if (settings_notifications.all_notifications.settings.stream_notification_settings.indexOf(
-        notification_name) !== -1) {
+    if (
+        settings_notifications.all_notifications.settings.stream_notification_settings.includes(
+            notification_name
+        )
+    ) {
         notification_name = notification_name.replace("enable_stream_", "");
         stream_ui_updates.update_notification_setting_checkbox(notification_name);
     }
diff --git a/static/js/people.js b/static/js/people.js
index f4e5983cf2..4f40692350 100644
--- a/static/js/people.js
+++ b/static/js/people.js
@@ -1050,10 +1050,8 @@ function safe_lower(s) {
 exports.matches_user_settings_search = function (person, value) {
     const email = exports.email_for_user_settings(person);
 
-    return (
-        safe_lower(person.full_name).indexOf(value) >= 0 ||
-        safe_lower(email).indexOf(value) >= 0
-    );
+    return safe_lower(person.full_name).includes(value) ||
+    safe_lower(email).includes(value);
 };
 
 exports.filter_for_user_settings_search = function (persons, query) {
diff --git a/static/js/pm_list.js b/static/js/pm_list.js
index 1c96076e09..7ebe24f2e7 100644
--- a/static/js/pm_list.js
+++ b/static/js/pm_list.js
@@ -64,7 +64,7 @@ exports._get_convos = function () {
 
         const num_unread = unread.num_unread_for_person(user_ids_string);
 
-        const is_group = user_ids_string.indexOf(',') >= 0;
+        const is_group = user_ids_string.includes(',');
 
         const is_active = user_ids_string === active_user_ids_string;
 
diff --git a/static/js/portico/integrations.js b/static/js/portico/integrations.js
index ab4e164a5f..89fbeab176 100644
--- a/static/js/portico/integrations.js
+++ b/static/js/portico/integrations.js
@@ -115,7 +115,7 @@ const update_integrations = _.debounce(function () {
             const display_name = INTEGRATIONS[$integration.data('name')];
             const display =
                 common.phrase_match(state.query, display_name) &&
-                ($integration.data('categories').indexOf(CATEGORIES[state.category]) !== -1 ||
+                ($integration.data('categories').includes(CATEGORIES[state.category]) ||
                  state.category === 'all');
 
             if (display) {
diff --git a/static/js/portico/landing-page.js b/static/js/portico/landing-page.js
index 6243e36e18..146d5ac24f 100644
--- a/static/js/portico/landing-page.js
+++ b/static/js/portico/landing-page.js
@@ -73,7 +73,7 @@ const apps_events = function () {
         const parts = path_parts();
 
         Object.keys(info).forEach(function (version) {
-            if (parts.indexOf(version) !== -1) {
+            if (parts.includes(version)) {
                 result = version;
             }
         });
@@ -160,11 +160,11 @@ const events = function () {
         e.stopPropagation();
     });
 
-    if (path_parts().indexOf("apps") !== -1) {
+    if (path_parts().includes("apps")) {
         apps_events();
     }
 
-    if (path_parts().indexOf('hello') !== -1) {
+    if (path_parts().includes('hello')) {
         hello_events();
     }
 };
diff --git a/static/js/portico/tabbed-instructions.js b/static/js/portico/tabbed-instructions.js
index 3340de385b..f33c50abfa 100644
--- a/static/js/portico/tabbed-instructions.js
+++ b/static/js/portico/tabbed-instructions.js
@@ -30,7 +30,7 @@ export function activate_correct_tab($codeSection) {
             $(this).addClass("active");
         }
 
-        if (desktop_os.indexOf(user_os) !== -1 && language === "desktop-web") {
+        if (desktop_os.includes(user_os) && language === "desktop-web") {
             $(this).addClass("active");
         }
     });
@@ -42,7 +42,7 @@ export function activate_correct_tab($codeSection) {
             $(this).addClass("active");
         }
 
-        if (desktop_os.indexOf(user_os) !== -1 && language === "desktop-web") {
+        if (desktop_os.includes(user_os) && language === "desktop-web") {
             $(this).addClass("active");
         }
     });
diff --git a/static/js/reactions.js b/static/js/reactions.js
index 82e8ad2863..c204cb9f68 100644
--- a/static/js/reactions.js
+++ b/static/js/reactions.js
@@ -432,7 +432,7 @@ exports.get_message_reactions = function (message) {
             reaction.is_realm_emoji = true;
             reaction.url = emoji.all_realm_emojis.get(reaction.emoji_code).emoji_url;
         }
-        if (reaction.user_ids.indexOf(page_params.user_id) !== -1) {
+        if (reaction.user_ids.includes(page_params.user_id)) {
             reaction.class = "message_reaction reacted";
         } else {
             reaction.class = "message_reaction";
diff --git a/static/js/rtl.js b/static/js/rtl.js
index c19877b897..0392d75cf8 100644
--- a/static/js/rtl.js
+++ b/static/js/rtl.js
@@ -65,10 +65,10 @@ const lr_ranges = convert_from_raw(digits, 2, '0$0}151u1<1<1|1|2222282u2w2!2#7Q7
  * @returns {'I' | 'PDI' | 'R' | 'L' | 'Other'}
  */
 function get_bidi_class(ch) {
-    if (i_chars.indexOf(ch) !== -1) {
+    if (i_chars.includes(ch)) {
         return 'I'; // LRI, RLI, FSI
     }
-    if (pdi_chars.indexOf(ch) !== -1) {
+    if (pdi_chars.includes(ch)) {
         return 'PDI';
     }
     let i = util.lower_bound(rl_ranges, ch);
diff --git a/static/js/search_suggestion.js b/static/js/search_suggestion.js
index 3829c5d786..6f5e1c8cf0 100644
--- a/static/js/search_suggestion.js
+++ b/static/js/search_suggestion.js
@@ -28,7 +28,7 @@ function match_criteria(operators, criteria) {
 function check_validity(last, operators, valid, invalid) {
     // valid: list of strings valid for the last operator
     // invalid: list of operators invalid for any previous operators except last.
-    if (valid.indexOf(last.operator) === -1) {
+    if (!valid.includes(last.operator)) {
         return false;
     }
     if (match_criteria(operators, invalid)) {
@@ -658,7 +658,7 @@ exports.get_search_result = function (base_query, query) {
     // will be deleted and new last will become {operator:'sender', operand: 'Ted sm`....}.
     if (query_operators_len > 1 &&
         last.operator === 'search' &&
-        person_suggestion_ops.indexOf(query_operators[query_operators_len - 2].operator) !== -1) {
+        person_suggestion_ops.includes(query_operators[query_operators_len - 2].operator)) {
         const person_op = query_operators[query_operators_len - 2];
         if (!people.reply_to_to_user_ids_string(person_op.operand)) {
             last = {
@@ -749,7 +749,7 @@ exports.get_search_result_legacy = function (query) {
     // will be deleted and new last will become {operator:'sender', operand: 'Ted sm`....}.
     if (operators_len > 1 &&
         last.operator === 'search' &&
-        person_suggestion_ops.indexOf(operators[operators_len - 2].operator) !== -1) {
+        person_suggestion_ops.includes(operators[operators_len - 2].operator)) {
         const person_op = operators[operators_len - 2];
         if (!people.reply_to_to_user_ids_string(person_op.operand)) {
             last = {
diff --git a/static/js/search_util.js b/static/js/search_util.js
index 6ebd410e0f..0bb732d030 100644
--- a/static/js/search_util.js
+++ b/static/js/search_util.js
@@ -18,7 +18,7 @@ exports.vanilla_match = function (opts) {
     */
     const val = opts.val.toLowerCase();
     return _.any(opts.search_terms, function (term) {
-        if (val.indexOf(term) !== -1) {
+        if (val.includes(term)) {
             return true;
         }
     });
diff --git a/static/js/settings_display.js b/static/js/settings_display.js
index 3e6b4f2f44..4f2e212b84 100644
--- a/static/js/settings_display.js
+++ b/static/js/settings_display.js
@@ -82,7 +82,7 @@ exports.set_up = function () {
             const data = {};
             data[setting] = JSON.stringify($(this).prop('checked'));
 
-            if (["left_side_userlist"].indexOf(setting) > -1) {
+            if (["left_side_userlist"].includes(setting)) {
                 change_display_setting(
                     data,
                     "#display-settings-status",
diff --git a/static/js/settings_emoji.js b/static/js/settings_emoji.js
index aea3bfcc0b..d6f7113bc0 100644
--- a/static/js/settings_emoji.js
+++ b/static/js/settings_emoji.js
@@ -77,7 +77,7 @@ exports.populate_emoji = function (emoji_data) {
         filter: {
             element: emoji_table.closest(".settings-section").find(".search"),
             predicate: function (item, value) {
-                return item.name.toLowerCase().indexOf(value) >= 0;
+                return item.name.toLowerCase().includes(value);
             },
             onupdate: function () {
                 ui.reset_scrollbar(emoji_table);
diff --git a/static/js/settings_exports.js b/static/js/settings_exports.js
index 67ad99c5ad..1dcca37106 100644
--- a/static/js/settings_exports.js
+++ b/static/js/settings_exports.js
@@ -47,7 +47,7 @@ exports.populate_exports_table = function (exports) {
         filter: {
             element: exports_table.closest(".settings-section").find(".search"),
             predicate: function (item, value) {
-                return people.get_full_name(item.acting_user_id).toLowerCase().indexOf(value) >= 0;
+                return people.get_full_name(item.acting_user_id).toLowerCase().includes(value);
             },
             onupdate: function () {
                 ui.reset_scrollbar(exports_table);
diff --git a/static/js/settings_invites.js b/static/js/settings_invites.js
index e4884ceb09..31ea5a26f6 100644
--- a/static/js/settings_invites.js
+++ b/static/js/settings_invites.js
@@ -64,11 +64,11 @@ function populate_invites(invites_data) {
             filter: {
                 element: invites_table.closest(".settings-section").find(".search"),
                 predicate: function (item, value) {
-                    const referrer_email_matched = item.ref.toLowerCase().indexOf(value) >= 0;
+                    const referrer_email_matched = item.ref.toLowerCase().includes(value);
                     if (item.is_multiuse) {
                         return referrer_email_matched;
                     }
-                    const invitee_email_matched = item.email.toLowerCase().indexOf(value) >= 0;
+                    const invitee_email_matched = item.email.toLowerCase().includes(value);
                     return referrer_email_matched || invitee_email_matched;
                 },
             },
diff --git a/static/js/settings_linkifiers.js b/static/js/settings_linkifiers.js
index 9506615a83..909c4754d2 100644
--- a/static/js/settings_linkifiers.js
+++ b/static/js/settings_linkifiers.js
@@ -38,10 +38,8 @@ exports.populate_filters = function (filters_data) {
         filter: {
             element: filters_table.closest(".settings-section").find(".search"),
             predicate: function (item, value) {
-                return (
-                    item[0].toLowerCase().indexOf(value) >= 0 ||
-                    item[1].toLowerCase().indexOf(value) >= 0
-                );
+                return item[0].toLowerCase().includes(value) ||
+                item[1].toLowerCase().includes(value);
             },
             onupdate: function () {
                 ui.reset_scrollbar(filters_table);
diff --git a/static/js/settings_org.js b/static/js/settings_org.js
index ba0c58bc2a..744233d2d6 100644
--- a/static/js/settings_org.js
+++ b/static/js/settings_org.js
@@ -463,7 +463,7 @@ exports.populate_notifications_stream_dropdown = function (stream_list) {
         filter: {
             element: search_input,
             predicate: function (item, value) {
-                return item.name.toLowerCase().indexOf(value) >= 0;
+                return item.name.toLowerCase().includes(value);
             },
             onupdate: function () {
                 ui.reset_scrollbar(dropdown_list_body);
@@ -492,7 +492,7 @@ exports.populate_signup_notifications_stream_dropdown = function (stream_list) {
         filter: {
             element: search_input,
             predicate: function (item, value) {
-                return item.name.toLowerCase().indexOf(value) >= 0;
+                return item.name.toLowerCase().includes(value);
             },
         },
     }).init();
@@ -507,7 +507,7 @@ exports.populate_signup_notifications_stream_dropdown = function (stream_list) {
 };
 
 function update_dependent_subsettings(property_name) {
-    if (simple_dropdown_properties.indexOf(property_name) !== -1) {
+    if (simple_dropdown_properties.includes(property_name)) {
         set_property_dropdown_value(property_name);
     } else if (property_name === 'realm_waiting_period_threshold') {
         set_realm_waiting_period_dropdown();
diff --git a/static/js/settings_streams.js b/static/js/settings_streams.js
index f1e6576b29..940fab56e9 100644
--- a/static/js/settings_streams.js
+++ b/static/js/settings_streams.js
@@ -38,7 +38,7 @@ exports.build_default_stream_table = function (streams_data) {
         filter: {
             element: table.closest(".settings-section").find(".search"),
             predicate: function (item, value) {
-                return item.name.toLowerCase().indexOf(value) >= 0;
+                return item.name.toLowerCase().includes(value);
             },
             onupdate: function () {
                 ui.reset_scrollbar(table);
diff --git a/static/js/settings_users.js b/static/js/settings_users.js
index 1991cc81a2..077f839443 100644
--- a/static/js/settings_users.js
+++ b/static/js/settings_users.js
@@ -174,10 +174,8 @@ function populate_users(realm_people_data) {
         filter: {
             element: $bots_table.closest(".settings-section").find(".search"),
             predicate: function (item, value) {
-                return (
-                    item.full_name.toLowerCase().indexOf(value) >= 0 ||
-                    item.email.toLowerCase().indexOf(value) >= 0
-                );
+                return item.full_name.toLowerCase().includes(value) ||
+                item.email.toLowerCase().includes(value);
             },
             onupdate: reset_scrollbar($bots_table),
         },
diff --git a/static/js/stream_create.js b/static/js/stream_create.js
index 5ad48184ad..e8d1251617 100644
--- a/static/js/stream_create.js
+++ b/static/js/stream_create.js
@@ -127,7 +127,7 @@ function ajaxSubscribeForCreation(stream_name, description, user_ids, invite_onl
         },
         error: function (xhr) {
             const msg = JSON.parse(xhr.responseText).msg;
-            if (msg.indexOf('access') >= 0) {
+            if (msg.includes('access')) {
                 // If we can't access the stream, we can safely assume it's
                 // a duplicate stream that we are not invited to.
                 stream_name_error.report_already_exists(stream_name);
@@ -210,7 +210,7 @@ function create_stream() {
     // Even though we already check to make sure that while typing the user cannot enter
     // newline characters (by pressing the enter key) it would still be possible to copy
     // and paste over a description with newline characters in it. Prevent that.
-    if (description.indexOf('\n') !== -1) {
+    if (description.includes('\n')) {
         ui_report.message(i18n.t("The stream description cannot contain newline characters."), $(".stream_create_info"), 'alert-error');
         return;
     }
@@ -409,7 +409,7 @@ exports.set_up_handlers = function () {
             stream_subscription_error.report_no_subs_to_stream();
             return;
         }
-        if (principals.indexOf(people.my_current_user_id()) < 0 && !page_params.is_admin) {
+        if (!principals.includes(people.my_current_user_id()) && !page_params.is_admin) {
             stream_subscription_error.cant_create_stream_without_susbscribing();
             return;
         }
diff --git a/static/js/stream_edit.js b/static/js/stream_edit.js
index dd012cc4cd..8ed07d1b5d 100644
--- a/static/js/stream_edit.js
+++ b/static/js/stream_edit.js
@@ -141,7 +141,7 @@ exports.sort_but_pin_current_user_on_top = function (emails) {
         return;
     }
     // Set current user top of subscription list, if subscribed.
-    if (emails.indexOf(people.my_current_email()) > -1) {
+    if (emails.includes(people.my_current_email())) {
         emails.splice(emails.indexOf(people.my_current_email()), 1);
         emails.sort();
         emails.unshift(people.my_current_email());
@@ -187,7 +187,7 @@ function show_subscription_settings(sub_row) {
                     const email = person.email.toLocaleLowerCase();
                     const full_name = person.full_name.toLowerCase();
 
-                    return email.indexOf(value) > -1 || full_name.indexOf(value) > -1;
+                    return email.includes(value) || full_name.includes(value);
                 }
             },
         },
@@ -205,8 +205,8 @@ function show_subscription_settings(sub_row) {
                 return false;
             }
             // Case-insensitive.
-            const item_matches = item.email.toLowerCase().indexOf(query) !== -1 ||
-                               item.full_name.toLowerCase().indexOf(query) !== -1;
+            const item_matches = item.email.toLowerCase().includes(query) ||
+                               item.full_name.toLowerCase().includes(query);
             const is_subscribed = stream_data.is_user_subscribed(sub.name, item.user_id);
             return item_matches && !is_subscribed;
         },
@@ -222,9 +222,9 @@ function show_subscription_settings(sub_row) {
 }
 
 exports.is_notification_setting = function (setting_label) {
-    if (setting_label.indexOf("_notifications") > -1) {
+    if (setting_label.includes("_notifications")) {
         return true;
-    } else if (setting_label.indexOf("_notify") > -1) {
+    } else if (setting_label.includes("_notify")) {
         return true;
     }
     return false;
diff --git a/static/js/ui.js b/static/js/ui.js
index 0f28ad953e..9477ab4b1e 100644
--- a/static/js/ui.js
+++ b/static/js/ui.js
@@ -165,7 +165,7 @@ exports.maybe_show_deprecation_notice = function (key) {
         }
     }
 
-    if (shown_deprecation_notices.indexOf(key) === -1) {
+    if (!shown_deprecation_notices.includes(key)) {
         $('#deprecation-notice-modal').modal('show');
         $('#deprecation-notice-message').text(message);
         $('#close-deprecation-notice').focus();
diff --git a/static/js/upload_widget.js b/static/js/upload_widget.js
index a082eaca3e..956bc3c848 100644
--- a/static/js/upload_widget.js
+++ b/static/js/upload_widget.js
@@ -12,7 +12,7 @@ function is_image_format(file) {
     if (!type) {
         return false;
     }
-    return supported_types.indexOf(type) >= 0;
+    return supported_types.includes(type);
 }
 
 exports.build_widget = function (
diff --git a/static/js/user_pill.js b/static/js/user_pill.js
index 7025408706..88cf95cfcf 100644
--- a/static/js/user_pill.js
+++ b/static/js/user_pill.js
@@ -9,7 +9,7 @@ exports.create_item_from_email = function (email, current_items) {
         if (page_params.realm_is_zephyr_mirror_realm) {
             const existing_emails = _.pluck(current_items, 'email');
 
-            if (existing_emails.indexOf(email) >= 0) {
+            if (existing_emails.includes(email)) {
                 return;
             }
 
@@ -28,7 +28,7 @@ exports.create_item_from_email = function (email, current_items) {
 
     const existing_ids = _.pluck(current_items, 'user_id');
 
-    if (existing_ids.indexOf(user.user_id) >= 0) {
+    if (existing_ids.includes(user.user_id)) {
         return;
     }
 
@@ -95,7 +95,7 @@ exports.typeahead_source = function (pill_widget) {
 exports.filter_taken_users = function (items, pill_widget) {
     const taken_user_ids = exports.get_user_ids(pill_widget);
     items = _.filter(items, function (item) {
-        return taken_user_ids.indexOf(item.user_id) === -1;
+        return !taken_user_ids.includes(item.user_id);
     });
     return items;
 };
@@ -134,8 +134,8 @@ exports.set_up_typeahead_on_pills = function (input, pills, update_func) {
         matcher: function (item) {
             let query = this.query.toLowerCase();
             query = query.replace(/\u00A0/g, String.fromCharCode(32));
-            return item.email.toLowerCase().indexOf(query) !== -1
-                    || item.full_name.toLowerCase().indexOf(query) !== -1;
+            return item.email.toLowerCase().includes(query)
+                    || item.full_name.toLowerCase().includes(query);
         },
         sorter: function (matches) {
             return typeahead_helper.sort_recipientbox_typeahead(
diff --git a/static/js/util.js b/static/js/util.js
index e84f227603..eb33aca8d8 100644
--- a/static/js/util.js
+++ b/static/js/util.js
@@ -67,7 +67,7 @@ exports.same_stream_and_topic = function util_same_stream_and_topic(a, b) {
 
 exports.is_pm_recipient = function (email, message) {
     const recipients = message.reply_to.toLowerCase().split(',');
-    return recipients.indexOf(email.toLowerCase()) !== -1;
+    return recipients.includes(email.toLowerCase());
 };
 
 exports.extract_pm_recipients = function (recipients) {
diff --git a/static/js/zcommand.js b/static/js/zcommand.js
index fe1e137839..3af04bbdf0 100644
--- a/static/js/zcommand.js
+++ b/static/js/zcommand.js
@@ -111,13 +111,13 @@ exports.process = function (message_content) {
     }
 
     const day_commands = ['/day', '/light'];
-    if (day_commands.indexOf(content) >= 0) {
+    if (day_commands.includes(content)) {
         exports.enter_day_mode();
         return true;
     }
 
     const night_commands = ['/night', '/dark'];
-    if (night_commands.indexOf(content) >= 0) {
+    if (night_commands.includes(content)) {
         exports.enter_night_mode();
         return true;
     }
diff --git a/static/shared/js/typeahead.js b/static/shared/js/typeahead.js
index b0f20d9f49..0f71b1fb04 100644
--- a/static/shared/js/typeahead.js
+++ b/static/shared/js/typeahead.js
@@ -64,7 +64,7 @@ function query_matches_string(query, source_str, split_char) {
     }
 
     // For a single token, the match can be anywhere in the string.
-    return source_str.indexOf(query) !== -1;
+    return source_str.includes(query);
 }
 
 // This function attempts to match a query with source's attributes.
diff --git a/tools/check-openapi b/tools/check-openapi
index b2ae6d77c5..ee4ee01401 100755
--- a/tools/check-openapi
+++ b/tools/check-openapi
@@ -9,7 +9,7 @@ function check_duplicate_operationids(file, api) {
         for (const value of endpoint) {
             const operation_id = value.operationId;
             if (operation_id !== undefined) {
-                if (operation_ids.indexOf(operation_id) >= 0) {
+                if (operation_ids.includes(operation_id)) {
                     console.error('In', file + ':');
                     console.error('Duplicate operationId:', operation_id);
                     process.exitCode = 1;
diff --git a/tools/linter_lib/custom_check.py b/tools/linter_lib/custom_check.py
index e2f09b2d68..20441a9cd1 100644
--- a/tools/linter_lib/custom_check.py
+++ b/tools/linter_lib/custom_check.py
@@ -132,9 +132,6 @@ js_rules = RuleList(
          'description': 'Do not concatenate i18n strings'},
         {'pattern': r'\+.*i18n\.t\(.+\)',
          'description': 'Do not concatenate i18n strings'},
-        {'pattern': '[.]includes[(]',
-         'exclude': {'frontend_tests/'},
-         'description': '.includes() is incompatible with Internet Explorer. Use .indexOf() !== -1 instead.'},
         {'pattern': '[.]html[(]',
          'exclude_pattern': r'''[.]html[(]("|'|render_|html|message.content|sub.rendered_description|i18n.t|rendered_|$|[)]|error_text|widget_elem|[$]error|[$][(]"<p>"[)])''',
          'exclude': {'static/js/portico', 'static/js/lightbox.js', 'static/js/ui_report.js',