diff --git a/tools/test-js-with-node b/tools/test-js-with-node
index 4829eefb0c..51e8423968 100755
--- a/tools/test-js-with-node
+++ b/tools/test-js-with-node
@@ -182,7 +182,7 @@ EXEMPT_FILES = make_set(
         "web/src/reload.js",
         "web/src/reload_setup.js",
         "web/src/reminder.js",
-        "web/src/resize.js",
+        "web/src/resize.ts",
         "web/src/resize_handler.js",
         "web/src/rows.ts",
         "web/src/scheduled_messages.ts",
diff --git a/web/src/resize.js b/web/src/resize.ts
similarity index 75%
rename from web/src/resize.js
rename to web/src/resize.ts
index ef441a989a..4e112811bf 100644
--- a/web/src/resize.js
+++ b/web/src/resize.ts
@@ -1,21 +1,24 @@
 import autosize from "autosize";
 import $ from "jquery";
+import assert from "minimalistic-assert";
 
 import * as blueslip from "./blueslip";
 import * as compose_state from "./compose_state";
 import * as compose_ui from "./compose_ui";
 import * as message_viewport from "./message_viewport";
 
-function get_bottom_whitespace_height() {
+function get_bottom_whitespace_height(): number {
     return message_viewport.height() * 0.4;
 }
 
-function get_new_heights() {
-    const res = {};
+function get_new_heights(): {
+    stream_filters_max_height: number;
+    buddy_list_wrapper_max_height: number;
+} {
     const viewport_height = message_viewport.height();
     const right_sidebar_shortcuts_height = $(".right-sidebar-shortcuts").outerHeight(true) ?? 0;
 
-    res.stream_filters_max_height =
+    let stream_filters_max_height =
         viewport_height -
         Number.parseInt($("#left-sidebar").css("paddingTop"), 10) -
         Number.parseInt($("#left-sidebar-navigation-area").css("marginTop"), 10) -
@@ -24,7 +27,7 @@ function get_new_heights() {
         ($("#private_messages_sticky_header").outerHeight(true) ?? 0);
 
     // Don't let us crush the stream sidebar completely out of view
-    res.stream_filters_max_height = Math.max(80, res.stream_filters_max_height);
+    stream_filters_max_height = Math.max(80, stream_filters_max_height);
 
     // RIGHT SIDEBAR
 
@@ -35,12 +38,15 @@ function get_new_heights() {
         ($("#user_search_section").outerHeight(true) ?? 0) -
         right_sidebar_shortcuts_height;
 
-    res.buddy_list_wrapper_max_height = Math.max(80, usable_height);
+    const buddy_list_wrapper_max_height = Math.max(80, usable_height);
 
-    return res;
+    return {
+        stream_filters_max_height,
+        buddy_list_wrapper_max_height,
+    };
 }
 
-export function watch_manual_resize(element) {
+export function watch_manual_resize(element: string): (() => void)[] | undefined {
     const box = document.querySelector(element);
 
     if (!box) {
@@ -48,27 +54,24 @@ export function watch_manual_resize(element) {
         return undefined;
     }
 
-    const meta = {
-        box,
-        height: null,
-        mousedown: false,
-    };
+    let height: number;
+    let mousedown = false;
 
-    const box_handler = function () {
-        meta.mousedown = true;
-        meta.height = meta.box.clientHeight;
+    const box_handler = function (): void {
+        mousedown = true;
+        height = box.clientHeight;
     };
-    meta.box.addEventListener("mousedown", box_handler);
+    box.addEventListener("mousedown", box_handler);
 
     // If the user resizes the textarea manually, we use the
     // callback to stop autosize from adjusting the height.
     // It will be re-enabled when this component is next opened.
-    const body_handler = function () {
-        if (meta.mousedown === true) {
-            meta.mousedown = false;
-            if (meta.height !== meta.box.clientHeight) {
-                meta.height = meta.box.clientHeight;
-                autosize.destroy($(element)).height(meta.height + "px");
+    const body_handler = function (): void {
+        if (mousedown) {
+            mousedown = false;
+            if (height !== box.clientHeight) {
+                height = box.clientHeight;
+                autosize.destroy($(element)).height(height + "px");
             }
         }
     };
@@ -77,7 +80,7 @@ export function watch_manual_resize(element) {
     return [box_handler, body_handler];
 }
 
-export function reset_compose_message_max_height(bottom_whitespace_height) {
+export function reset_compose_message_max_height(bottom_whitespace_height: number): void {
     // If the compose-box is open, we set the `max-height` property of
     // `compose-textarea` and `preview-textarea`, so that the
     // compose-box's maximum extent does not overlap the last message
@@ -89,10 +92,10 @@ export function reset_compose_message_max_height(bottom_whitespace_height) {
         bottom_whitespace_height = get_bottom_whitespace_height();
     }
 
-    const compose_height = $("#compose").get(0).getBoundingClientRect().height;
+    const compose_height = $("#compose").get(0)!.getBoundingClientRect().height;
     const compose_textarea_height = Math.max(
-        $("textarea#compose-textarea").get(0).getBoundingClientRect().height,
-        $("#preview_message_area").get(0).getBoundingClientRect().height,
+        $("textarea#compose-textarea").get(0)!.getBoundingClientRect().height,
+        $("#preview_message_area").get(0)!.getBoundingClientRect().height,
     );
     const compose_non_textarea_height = compose_height - compose_textarea_height;
 
@@ -112,7 +115,7 @@ export function reset_compose_message_max_height(bottom_whitespace_height) {
     $("#scroll-to-bottom-button-container").css("bottom", compose_height);
 }
 
-export function resize_bottom_whitespace() {
+export function resize_bottom_whitespace(): void {
     const bottom_whitespace_height = get_bottom_whitespace_height();
     $("html").css("--max-unexpanded-compose-height", `${bottom_whitespace_height}px`);
     // The height of the compose box is tied to that of
@@ -126,7 +129,7 @@ export function resize_bottom_whitespace() {
     }
 }
 
-export function resize_stream_subscribers_list() {
+export function resize_stream_subscribers_list(): void {
     // Calculates the height of the subscribers list in stream settings.
     // This avoids the stream settings from overflowing the container and
     // having a scroll bar.
@@ -149,36 +152,40 @@ export function resize_stream_subscribers_list() {
     );
     let total_height_of_classes_above_subscribers_list = 0;
     $classes_above_subscribers_list.each(function () {
-        total_height_of_classes_above_subscribers_list += $(this).outerHeight(true);
+        const outer_height = $(this).outerHeight(true);
+        assert(outer_height !== undefined);
+        total_height_of_classes_above_subscribers_list += outer_height;
     });
     const subscribers_list_header_height = 30;
     const margin_between_tab_switcher_and_add_subscribers_title = 20;
+    const subscriptions_info_height = $subscriptions_info.height();
+    assert(subscriptions_info_height !== undefined);
     const subscribers_list_height =
-        $subscriptions_info.height() -
+        subscriptions_info_height -
         total_height_of_classes_above_subscribers_list -
         subscribers_list_header_height -
         margin_between_tab_switcher_and_add_subscribers_title;
     $("html").css("--stream-subscriber-list-max-height", `${subscribers_list_height}px`);
 }
 
-export function resize_stream_filters_container() {
+export function resize_stream_filters_container(): void {
     const h = get_new_heights();
     resize_bottom_whitespace();
     $("#left_sidebar_scroll_container").css("max-height", h.stream_filters_max_height);
 }
 
-export function resize_sidebars() {
+export function resize_sidebars(): void {
     const h = get_new_heights();
     $("#buddy_list_wrapper").css("max-height", h.buddy_list_wrapper_max_height);
     $("#left_sidebar_scroll_container").css("max-height", h.stream_filters_max_height);
 }
 
-export function update_recent_view_filters_height() {
+export function update_recent_view_filters_height(): void {
     const recent_view_filters_height = $("#recent_view_filter_buttons").outerHeight(true) ?? 0;
     $("html").css("--recent-topics-filters-height", `${recent_view_filters_height}px`);
 }
 
-function resize_navbar_alerts() {
+function resize_navbar_alerts(): void {
     const navbar_alerts_height = $("#navbar_alerts_wrapper").height();
     document.documentElement.style.setProperty(
         "--navbar-alerts-wrapper-height",
@@ -192,7 +199,7 @@ function resize_navbar_alerts() {
     }
 }
 
-export function resize_page_components() {
+export function resize_page_components(): void {
     resize_navbar_alerts();
     resize_sidebars();
     resize_bottom_whitespace();
diff --git a/web/styles/zulip.css b/web/styles/zulip.css
index 3319485f46..1d2f6801f9 100644
--- a/web/styles/zulip.css
+++ b/web/styles/zulip.css
@@ -151,7 +151,7 @@ body {
     --browser-overlay-scrollbar-width: 10px;
 
     /* This is a rough estimate for height occupied by Recent Conversations filters.
-       We expect `resize.js` to update this once UI is initialized. */
+       We expect `resize.ts` to update this once UI is initialized. */
     --recent-topics-filters-height: 50px;
 
     /* Overlay heights for streams modal */
@@ -166,7 +166,7 @@ body {
 
     /*
     Maximum height of the compose box when it is not in expanded state. This
-    is equal to the height of `#bottom_whitespace`. We expect resize.js to
+    is equal to the height of `#bottom_whitespace`. We expect resize.ts to
     replace it with its pixel calculation since even if `vh` has great support,
     it can change depending on browser / OS on mobile devices.
     */