diff --git a/tools/test-js-with-node b/tools/test-js-with-node
index 82935c803f..fd6610e031 100755
--- a/tools/test-js-with-node
+++ b/tools/test-js-with-node
@@ -113,7 +113,7 @@ EXEMPT_FILES = make_set(
         "web/src/hotkey.js",
         "web/src/hotspots.js",
         "web/src/inbox_ui.js",
-        "web/src/inbox_util.js",
+        "web/src/inbox_util.ts",
         "web/src/info_overlay.js",
         "web/src/integration_url_modal.js",
         "web/src/invite.ts",
diff --git a/web/src/inbox_util.js b/web/src/inbox_util.ts
similarity index 82%
rename from web/src/inbox_util.js
rename to web/src/inbox_util.ts
index 24e8b34431..23360a767a 100644
--- a/web/src/inbox_util.js
+++ b/web/src/inbox_util.ts
@@ -5,15 +5,15 @@ import * as stream_data from "./stream_data";
 
 let is_inbox_visible = false;
 
-export function set_visible(value) {
+export function set_visible(value: boolean): void {
     is_inbox_visible = value;
 }
 
-export function is_visible() {
+export function is_visible(): boolean {
     return is_inbox_visible;
 }
 
-export function update_stream_colors() {
+export function update_stream_colors(): void {
     if (!is_visible()) {
         return;
     }
@@ -21,7 +21,7 @@ export function update_stream_colors() {
     const $stream_headers = $("#inbox-streams-container .inbox-header");
     $stream_headers.each((_index, stream_header) => {
         const $stream_header = $(stream_header);
-        const stream_id = Number.parseInt($stream_header.attr("data-stream-id"), 10);
+        const stream_id = Number.parseInt($stream_header.attr("data-stream-id")!, 10);
         if (!stream_id) {
             return;
         }