diff --git a/tools/test-js-with-node b/tools/test-js-with-node
index e1560e5aba..b3d192468d 100755
--- a/tools/test-js-with-node
+++ b/tools/test-js-with-node
@@ -232,7 +232,7 @@ EXEMPT_FILES = make_set(
         "web/src/stream_list.js",
         "web/src/stream_muting.js",
         "web/src/stream_popover.js",
-        "web/src/stream_settings_api.js",
+        "web/src/stream_settings_api.ts",
         "web/src/stream_settings_components.js",
         "web/src/stream_settings_containers.ts",
         "web/src/stream_settings_ui.js",
diff --git a/web/src/stream_settings_api.js b/web/src/stream_settings_api.js
deleted file mode 100644
index c070f36fe6..0000000000
--- a/web/src/stream_settings_api.js
+++ /dev/null
@@ -1,28 +0,0 @@
-import * as channel from "./channel";
-import * as settings_ui from "./settings_ui";
-import * as sub_store from "./sub_store";
-
-export function bulk_set_stream_property(sub_data, $status_element) {
-    const url = "/json/users/me/subscriptions/properties";
-    const data = {subscription_data: JSON.stringify(sub_data)};
-    if (!$status_element) {
-        return channel.post({
-            url,
-            data,
-            timeout: 10 * 1000,
-        });
-    }
-
-    settings_ui.do_settings_change(channel.post, url, data, $status_element);
-    return undefined;
-}
-
-export function set_stream_property(sub, data, $status_element) {
-    const sub_data = {stream_id: sub.stream_id, ...data};
-    bulk_set_stream_property([sub_data], $status_element);
-}
-
-export function set_color(stream_id, color) {
-    const sub = sub_store.get(stream_id);
-    set_stream_property(sub, {property: "color", value: color});
-}
diff --git a/web/src/stream_settings_api.ts b/web/src/stream_settings_api.ts
new file mode 100644
index 0000000000..e81c53fb77
--- /dev/null
+++ b/web/src/stream_settings_api.ts
@@ -0,0 +1,50 @@
+import assert from "minimalistic-assert";
+
+import * as channel from "./channel";
+import * as settings_ui from "./settings_ui";
+import type {StreamProperties, StreamSubscription} from "./sub_store";
+import * as sub_store from "./sub_store";
+
+export function bulk_set_stream_property(
+    sub_data: {
+        [Property in keyof StreamProperties]: {
+            stream_id: number;
+            property: Property;
+            value: StreamProperties[Property];
+        };
+    }[keyof StreamProperties][],
+    $status_element?: JQuery,
+): void {
+    const url = "/json/users/me/subscriptions/properties";
+    const data = {subscription_data: JSON.stringify(sub_data)};
+    if (!$status_element) {
+        return void channel.post({
+            url,
+            data,
+            timeout: 10 * 1000,
+        });
+    }
+
+    settings_ui.do_settings_change(channel.post, url, data, $status_element);
+    return undefined;
+}
+
+export function set_stream_property(
+    sub: StreamSubscription,
+    data: {
+        [Property in keyof StreamProperties]: {
+            property: Property;
+            value: StreamProperties[Property];
+        };
+    }[keyof StreamProperties],
+    $status_element?: JQuery,
+): void {
+    const sub_data = {stream_id: sub.stream_id, ...data};
+    bulk_set_stream_property([sub_data], $status_element);
+}
+
+export function set_color(stream_id: number, color: string): void {
+    const sub = sub_store.get(stream_id);
+    assert(sub !== undefined);
+    set_stream_property(sub, {property: "color", value: color});
+}
diff --git a/web/src/sub_store.ts b/web/src/sub_store.ts
index f514b5a03b..50dced51c2 100644
--- a/web/src/sub_store.ts
+++ b/web/src/sub_store.ts
@@ -39,12 +39,15 @@ export type NeverSubscribedStream = Stream & {
     subscribers?: number[];
 };
 
-// This is the raw data we get from the server for a subscription.
-export type ApiStreamSubscription = (Stream & StreamSpecificNotificationSettings) & {
+export type StreamProperties = StreamSpecificNotificationSettings & {
     color: string;
-    email_address: string;
     is_muted: boolean;
     pin_to_top: boolean;
+};
+
+// This is the raw data we get from the server for a subscription.
+export type ApiStreamSubscription = (Stream & StreamProperties) & {
+    email_address: string;
     stream_weekly_traffic: number | null;
     subscribers?: number[];
 };