ts: Migrate `feedback_widget` to TypeScript.

This commit migrates `feedback_widget` module to TypeScript.

tools/test-js-with-node

@@ -88,7 +88,7 @@ EXEMPT_FILES = make_set(
         "web/src/emoji_picker.js",
         "web/src/emojisets.js",
         "web/src/favicon.ts",
-        "web/src/feedback_widget.js",
+        "web/src/feedback_widget.ts",
         "web/src/flatpickr.js",
         "web/src/gear_menu.ts",
         "web/src/giphy.js",

web/src/feedback_widget.ts

@@ -22,7 +22,23 @@ Code-wise it's a singleton widget that controls the DOM inside
 
 */
 
-const meta = {
+type FeedbackWidgetMeta = {
+    hide_me_time: number | null;
+    alert_hover_state: boolean;
+    $container: JQuery | null;
+    opened: boolean;
+    handlers_set?: boolean;
+    undo?: () => void;
+};
+
+type FeedbackWidgetOptions = {
+    populate: (element: JQuery) => void;
+    title_text: string;
+    undo_button_text: string;
+    on_undo: () => void;
+};
+
+const meta: FeedbackWidgetMeta = {
     hide_me_time: null,
     alert_hover_state: false,
     $container: null,
@@ -35,12 +51,12 @@ const animate = {
             return;
         }
 
-        if (meta.hide_me_time < Date.now() && !meta.alert_hover_state) {
+        if ((meta.hide_me_time ?? 0) < Date.now() && !meta.alert_hover_state) {
             animate.fadeOut();
             return;
         }
 
-        setTimeout(animate.maybe_close, 100);
+        setTimeout(() => animate.maybe_close(), 100);
     },
     fadeOut() {
         if (!meta.opened) {
@@ -61,16 +77,21 @@ const animate = {
         if (meta.$container) {
             meta.$container.fadeIn(500).addClass("show");
             meta.opened = true;
-            setTimeout(animate.maybe_close, 100);
+            setTimeout(() => animate.maybe_close(), 100);
         }
     },
 };
 
-function set_up_handlers() {
+function set_up_handlers(): void {
     if (meta.handlers_set) {
         return;
     }
 
+    if (!meta.$container) {
+        blueslip.error("$container not found for feedback widget.");
+        return;
+    }
+
     meta.handlers_set = true;
 
     // if the user mouses over the notification, don't hide it.
@@ -91,7 +112,7 @@ function set_up_handlers() {
         meta.alert_hover_state = false;
         // add at least 2000ms but if more than that exists just keep the
         // current amount.
-        meta.hide_me_time = Math.max(meta.hide_me_time, Date.now() + 2000);
+        meta.hide_me_time = Math.max(meta.hide_me_time ?? 0, Date.now() + 2000);
     });
 
     meta.$container.on("click", ".exit-me", () => {
@@ -106,15 +127,15 @@ function set_up_handlers() {
     });
 }
 
-export function is_open() {
+export function is_open(): boolean {
     return meta.opened;
 }
 
-export function dismiss() {
+export function dismiss(): void {
     animate.fadeOut();
 }
 
-export function show(opts) {
+export function show(opts: FeedbackWidgetOptions): void {
     if (!opts.populate) {
         blueslip.error("programmer needs to supply populate callback.");
         return;
@@ -122,7 +143,7 @@ export function show(opts) {
 
     meta.$container = $("#feedback_container");
 
-    const html = render_feedback_container();
+    const html = render_feedback_container({});
     meta.$container.html(html);
 
     set_up_handlers();