diff --git a/tools/test-js-with-node b/tools/test-js-with-node
index dc9b852c79..5d7d495c34 100755
--- a/tools/test-js-with-node
+++ b/tools/test-js-with-node
@@ -117,7 +117,7 @@ EXEMPT_FILES = make_set(
         "web/src/hashchange.js",
         "web/src/hbs.d.ts",
         "web/src/hotkey.js",
-        "web/src/inbox_ui.js",
+        "web/src/inbox_ui.ts",
         "web/src/inbox_util.ts",
         "web/src/info_overlay.ts",
         "web/src/information_density.ts",
diff --git a/web/src/inbox_ui.js b/web/src/inbox_ui.ts
similarity index 75%
rename from web/src/inbox_ui.js
rename to web/src/inbox_ui.ts
index 9bf8f9d4e6..8b748b97bc 100644
--- a/web/src/inbox_ui.js
+++ b/web/src/inbox_ui.ts
@@ -1,5 +1,8 @@
 import $ from "jquery";
 import _ from "lodash";
+import assert from "minimalistic-assert";
+import type * as tippy from "tippy.js";
+import {z} from "zod";
 
 import render_inbox_row from "../templates/inbox_view/inbox_row.hbs";
 import render_inbox_stream_container from "../templates/inbox_view/inbox_stream_container.hbs";
@@ -19,6 +22,7 @@ import * as keydown_util from "./keydown_util";
 import * as left_sidebar_navigation_area from "./left_sidebar_navigation_area";
 import {localstorage} from "./localstorage";
 import * as message_store from "./message_store";
+import type {Message} from "./message_store";
 import * as modals from "./modals";
 import * as onboarding_steps from "./onboarding_steps";
 import * as overlays from "./overlays";
@@ -37,9 +41,103 @@ import * as user_topics_ui from "./user_topics_ui";
 import * as util from "./util";
 import * as views_util from "./views_util";
 
-let dms_dict = new Map();
-let topics_dict = new Map();
-let streams_dict = new Map();
+type DirectMessageContext = {
+    conversation_key: string;
+    is_direct: boolean;
+    rendered_dm_with: string;
+    is_group: boolean;
+    user_circle_class: string | false | undefined;
+    is_bot: boolean;
+    dm_url: string;
+    user_ids_string: string;
+    unread_count: number;
+    is_hidden: boolean;
+    is_collapsed: boolean;
+    latest_msg_id: number;
+};
+
+const direct_message_context_properties: (keyof DirectMessageContext)[] = [
+    "conversation_key",
+    "is_direct",
+    "rendered_dm_with",
+    "is_group",
+    "user_circle_class",
+    "is_bot",
+    "dm_url",
+    "user_ids_string",
+    "unread_count",
+    "is_hidden",
+    "is_collapsed",
+    "latest_msg_id",
+];
+
+type StreamContext = {
+    is_stream: boolean;
+    invite_only: boolean;
+    is_web_public: boolean;
+    stream_name: string;
+    pin_to_top: boolean | undefined;
+    is_muted: boolean;
+    stream_color: string;
+    stream_header_color: string;
+    stream_url: string;
+    stream_id: number;
+    is_hidden: boolean;
+    is_collapsed: boolean;
+    mention_in_unread: boolean;
+    unread_count?: number;
+};
+
+const stream_context_properties: (keyof StreamContext)[] = [
+    "is_stream",
+    "invite_only",
+    "is_web_public",
+    "stream_name",
+    "pin_to_top",
+    "is_muted",
+    "stream_color",
+    "stream_header_color",
+    "stream_url",
+    "stream_id",
+    "is_hidden",
+    "is_collapsed",
+    "mention_in_unread",
+    "unread_count",
+];
+
+type TopicContext = {
+    is_topic: boolean;
+    stream_id: number;
+    topic_name: string;
+    unread_count: number;
+    conversation_key: string;
+    topic_url: string;
+    is_hidden: boolean;
+    is_collapsed: boolean;
+    mention_in_unread: boolean;
+    latest_msg_id: number;
+    all_visibility_policies: typeof user_topics.all_visibility_policies;
+    visibility_policy: number | false;
+};
+
+const topic_context_properties: (keyof TopicContext)[] = [
+    "is_topic",
+    "stream_id",
+    "topic_name",
+    "unread_count",
+    "conversation_key",
+    "topic_url",
+    "is_hidden",
+    "is_collapsed",
+    "mention_in_unread",
+    "latest_msg_id",
+    "all_visibility_policies",
+    "visibility_policy",
+];
+
+let dms_dict = new Map<string, DirectMessageContext>();
+let topics_dict = new Map<string, Map<string, TopicContext>>();
+let streams_dict = new Map<string, StreamContext>();
 let update_triggered_by_user = false;
 let filters_dropdown_widget;
 
@@ -58,12 +156,12 @@ const ls_collapsed_containers_key = "inbox_collapsed_containers";
 
 const ls = localstorage();
 let filters = new Set([views_util.FILTERS.UNMUTED_TOPICS]);
-let collapsed_containers = new Set();
+let collapsed_containers = new Set<string>();
 
 let search_keyword = "";
 const INBOX_SEARCH_ID = "inbox-search";
 const INBOX_FILTERS_DROPDOWN_ID = "inbox-filter_widget";
-export let current_focus_id;
+export let current_focus_id: string | undefined;
 
 const STREAM_HEADER_PREFIX = "inbox-stream-header-";
 const CONVERSATION_ID_PREFIX = "inbox-row-conversation-";
@@ -71,16 +169,16 @@ const CONVERSATION_ID_PREFIX = "inbox-row-conversation-";
 const LEFT_NAVIGATION_KEYS = ["left_arrow", "shift_tab", "vim_left"];
 const RIGHT_NAVIGATION_KEYS = ["right_arrow", "tab", "vim_right"];
 
-function get_row_from_conversation_key(key) {
+function get_row_from_conversation_key(key: string): JQuery {
     return $(`#${CSS.escape(CONVERSATION_ID_PREFIX + key)}`);
 }
 
-function save_data_to_ls() {
+function save_data_to_ls(): void {
     ls.set(ls_filter_key, [...filters]);
     ls.set(ls_collapsed_containers_key, [...collapsed_containers]);
 }
 
-export function show() {
+export function show(): void {
     // Avoid setting col_focus to recipient when moving to inbox from other narrows.
     // We prefer to focus entire row instead of stream name for inbox-header.
     // Since inbox-row doesn't has a collapse button, focus on COLUMNS.COLLAPSE_BUTTON
@@ -109,7 +207,9 @@ export function show() {
             html_heading: $t_html({defaultMessage: "Welcome to your <b>inbox</b>!"}),
             html_body,
             html_submit_button: $t_html({defaultMessage: "Continue"}),
-            on_click() {},
+            on_click() {
+                // Do nothing
+            },
             single_footer_button: true,
             focus_submit_on_open: true,
         });
@@ -117,39 +217,39 @@ export function show() {
     }
 }
 
-export function hide() {
+export function hide(): void {
     views_util.hide({
         $view: $("#inbox-view"),
         set_visible,
     });
 }
 
-function get_topic_key(stream_id, topic) {
+function get_topic_key(stream_id: number, topic: string): string {
     return stream_id + ":" + topic;
 }
 
-function get_stream_key(stream_id) {
+function get_stream_key(stream_id: number): string {
     return "stream_" + stream_id;
 }
 
-function get_stream_container(stream_key) {
+function get_stream_container(stream_key: string): JQuery {
     return $(`#${CSS.escape(stream_key)}`);
 }
 
-function get_topics_container(stream_id) {
+function get_topics_container(stream_id: number): JQuery {
     const $topics_container = get_stream_header_row(stream_id)
         .next(".inbox-topic-container")
         .expectOne();
     return $topics_container;
 }
 
-function get_stream_header_row(stream_id) {
+function get_stream_header_row(stream_id: number): JQuery {
     const $stream_header_row = $(`#${CSS.escape(STREAM_HEADER_PREFIX + stream_id)}`);
     return $stream_header_row;
 }
 
-function load_data_from_ls() {
-    const saved_filters = new Set(ls.get(ls_filter_key));
+function load_data_from_ls(): void {
+    const saved_filters = new Set(z.array(z.string()).optional().parse(ls.get(ls_filter_key)));
     const valid_filters = new Set(Object.values(views_util.FILTERS));
     // If saved filters are not in the list of valid filters, we reset to default.
     const is_subset = [...saved_filters].every((filter) => valid_filters.has(filter));
@@ -158,10 +258,16 @@ function load_data_from_ls() {
     } else {
         filters = saved_filters;
     }
-    collapsed_containers = new Set(ls.get(ls_collapsed_containers_key));
+    collapsed_containers = new Set(
+        z.array(z.string()).optional().parse(ls.get(ls_collapsed_containers_key)),
+    );
 }
 
-function format_dm(user_ids_string, unread_count, latest_msg_id) {
+function format_dm(
+    user_ids_string: string,
+    unread_count: number,
+    latest_msg_id: number,
+): DirectMessageContext {
     const recipient_ids = people.user_ids_string_to_ids_array(user_ids_string);
     if (!recipient_ids.length) {
         // Self DM
@@ -169,6 +275,7 @@ function format_dm(user_ids_string, unread_count, latest_msg_id) {
     }
 
     const reply_to = people.user_ids_string_to_emails_string(user_ids_string);
+    assert(reply_to !== undefined);
     const rendered_dm_with = recipient_ids
         .map((recipient_id) => ({
             name: people.get_display_full_name(recipient_id),
@@ -177,7 +284,7 @@ function format_dm(user_ids_string, unread_count, latest_msg_id) {
         .sort((a, b) => util.strcmp(a.name, b.name))
         .map((user_info) => render_user_with_status_icon(user_info));
 
-    let user_circle_class;
+    let user_circle_class: string | false | undefined;
     let is_bot = false;
     if (recipient_ids.length === 1) {
         is_bot = people.get_by_user_id(recipient_ids[0]).is_bot;
@@ -202,7 +309,7 @@ function format_dm(user_ids_string, unread_count, latest_msg_id) {
     return context;
 }
 
-function insert_dms(keys_to_insert) {
+function insert_dms(keys_to_insert: string[]): void {
     const sorted_keys = [...dms_dict.keys()];
     // If we need to insert at the top, we do it separately to avoid edge case in loop below.
     if (keys_to_insert.includes(sorted_keys[0])) {
@@ -223,7 +330,11 @@ function insert_dms(keys_to_insert) {
     }
 }
 
-function rerender_dm_inbox_row_if_needed(new_dm_data, old_dm_data, dm_keys_to_insert) {
+function rerender_dm_inbox_row_if_needed(
+    new_dm_data: DirectMessageContext,
+    old_dm_data: DirectMessageContext | undefined,
+    dm_keys_to_insert: string[],
+): void {
     if (old_dm_data === undefined) {
         // This row is not rendered yet.
         dm_keys_to_insert.push(new_dm_data.conversation_key);
@@ -238,7 +349,7 @@ function rerender_dm_inbox_row_if_needed(new_dm_data, old_dm_data, dm_keys_to_in
     }
 
     // If row's latest_msg_id didn't change, we can inplace rerender it, if needed.
-    for (const property in new_dm_data) {
+    for (const property of direct_message_context_properties) {
         if (new_dm_data[property] !== old_dm_data[property]) {
             const $rendered_row = get_row_from_conversation_key(new_dm_data.conversation_key);
             $rendered_row.replaceWith($(render_inbox_row(new_dm_data)));
@@ -247,10 +358,11 @@ function rerender_dm_inbox_row_if_needed(new_dm_data, old_dm_data, dm_keys_to_in
     }
 }
 
-function format_stream(stream_id) {
+function format_stream(stream_id: number): StreamContext {
     // NOTE: Unread count is not included in this function as it is more
     // efficient for the callers to calculate it based on filters.
     const stream_info = sub_store.get(stream_id);
+    assert(stream_info !== undefined);
 
     return {
         is_stream: true,
@@ -270,28 +382,35 @@ function format_stream(stream_id) {
     };
 }
 
-function update_stream_data(stream_id, stream_key, topic_dict) {
-    topics_dict.set(stream_key, new Map());
+function update_stream_data(
+    stream_id: number,
+    stream_key: string,
+    topic_dict: Map<string, {topic_count: number; latest_msg_id: number}>,
+): void {
+    const stream_topics_data = new Map<string, TopicContext>();
     const stream_data = format_stream(stream_id);
     let stream_post_filter_unread_count = 0;
     for (const [topic, {topic_count, latest_msg_id}] of topic_dict) {
         const topic_key = get_topic_key(stream_id, topic);
         if (topic_count) {
             const topic_data = format_topic(stream_id, topic, topic_count, latest_msg_id);
-            topics_dict.get(stream_key).set(topic_key, topic_data);
+            stream_topics_data.set(topic_key, topic_data);
             if (!topic_data.is_hidden) {
                 stream_post_filter_unread_count += topic_data.unread_count;
             }
         }
     }
-    topics_dict.set(stream_key, get_sorted_row_dict(topics_dict.get(stream_key)));
+    topics_dict.set(stream_key, get_sorted_row_dict(stream_topics_data));
     stream_data.is_hidden = stream_post_filter_unread_count === 0;
     stream_data.unread_count = stream_post_filter_unread_count;
     streams_dict.set(stream_key, stream_data);
 }
 
-function rerender_stream_inbox_header_if_needed(new_stream_data, old_stream_data) {
-    for (const property in new_stream_data) {
+function rerender_stream_inbox_header_if_needed(
+    new_stream_data: StreamContext,
+    old_stream_data: StreamContext,
+): void {
+    for (const property of stream_context_properties) {
         if (new_stream_data[property] !== old_stream_data[property]) {
             const $rendered_row = get_stream_header_row(new_stream_data.stream_id);
             $rendered_row.replaceWith($(render_inbox_row(new_stream_data)));
@@ -300,7 +419,12 @@ function rerender_stream_inbox_header_if_needed(new_stream_data, old_stream_data
     }
 }
 
-function format_topic(stream_id, topic, topic_unread_count, latest_msg_id) {
+function format_topic(
+    stream_id: number,
+    topic: string,
+    topic_unread_count: number,
+    latest_msg_id: number,
+): TopicContext {
     const context = {
         is_topic: true,
         stream_id,
@@ -322,7 +446,10 @@ function format_topic(stream_id, topic, topic_unread_count, latest_msg_id) {
     return context;
 }
 
-function insert_stream(stream_id, topic_dict) {
+function insert_stream(
+    stream_id: number,
+    topic_dict: Map<string, {topic_count: number; latest_msg_id: number}>,
+): boolean {
     const stream_key = get_stream_key(stream_id);
     update_stream_data(stream_id, stream_key, topic_dict);
     const sorted_stream_keys = get_sorted_stream_keys();
@@ -338,11 +465,12 @@ function insert_stream(stream_id, topic_dict) {
         const previous_stream_key = sorted_stream_keys[stream_index - 1];
         $(rendered_stream).insertAfter(get_stream_container(previous_stream_key));
     }
-    return !streams_dict.get(stream_key).is_hidden;
+    return !streams_dict.get(stream_key)!.is_hidden;
 }
 
-function insert_topics(keys, stream_key) {
+function insert_topics(keys: string[], stream_key: string): void {
     const stream_topics_data = topics_dict.get(stream_key);
+    assert(stream_topics_data !== undefined);
     const sorted_keys = [...stream_topics_data.keys()];
     // If we need to insert at the top, we do it separately to avoid edge case in loop below.
     if (keys.includes(sorted_keys[0])) {
@@ -364,7 +492,11 @@ function insert_topics(keys, stream_key) {
     }
 }
 
-function rerender_topic_inbox_row_if_needed(new_topic_data, old_topic_data, topic_keys_to_insert) {
+function rerender_topic_inbox_row_if_needed(
+    new_topic_data: TopicContext,
+    old_topic_data: TopicContext | undefined,
+    topic_keys_to_insert: string[],
+): void {
     if (old_topic_data === undefined) {
         // This row is not rendered yet.
         topic_keys_to_insert.push(new_topic_data.conversation_key);
@@ -377,7 +509,7 @@ function rerender_topic_inbox_row_if_needed(new_topic_data, old_topic_data, topi
         topic_keys_to_insert.push(new_topic_data.conversation_key);
     }
 
-    for (const property in new_topic_data) {
+    for (const property of topic_context_properties) {
         if (new_topic_data[property] !== old_topic_data[property]) {
             const $rendered_row = get_row_from_conversation_key(new_topic_data.conversation_key);
             $rendered_row.replaceWith($(render_inbox_row(new_topic_data)));
@@ -386,10 +518,11 @@ function rerender_topic_inbox_row_if_needed(new_topic_data, old_topic_data, topi
     }
 }
 
-function get_sorted_stream_keys() {
-    function compare_function(a, b) {
+function get_sorted_stream_keys(): string[] {
+    function compare_function(a: string, b: string): number {
         const stream_a = streams_dict.get(a);
         const stream_b = streams_dict.get(b);
+        assert(stream_a !== undefined && stream_b !== undefined);
 
         // If one of the streams is pinned, they are sorted higher.
         if (stream_a.pin_to_top && !stream_b.pin_to_top) {
@@ -418,32 +551,28 @@ function get_sorted_stream_keys() {
     return [...topics_dict.keys()].sort(compare_function);
 }
 
-function get_sorted_stream_topic_dict() {
+function get_sorted_stream_topic_dict(): Map<string, Map<string, TopicContext>> {
     const sorted_stream_keys = get_sorted_stream_keys();
-    const sorted_topic_dict = new Map();
+    const sorted_topic_dict = new Map<string, Map<string, TopicContext>>();
     for (const sorted_stream_key of sorted_stream_keys) {
-        sorted_topic_dict.set(sorted_stream_key, topics_dict.get(sorted_stream_key));
+        sorted_topic_dict.set(sorted_stream_key, topics_dict.get(sorted_stream_key)!);
     }
 
     return sorted_topic_dict;
 }
 
-function get_sorted_row_keys(row_dict) {
-    return [...row_dict.keys()].sort(
-        (a, b) => row_dict.get(b).latest_msg_id - row_dict.get(a).latest_msg_id,
-    );
+function get_sorted_row_dict<T extends DirectMessageContext | TopicContext>(
+    row_dict: Map<string, T>,
+): Map<string, T> {
+    return new Map([...row_dict].sort(([, a], [, b]) => b.latest_msg_id - a.latest_msg_id));
 }
 
-function get_sorted_row_dict(row_dict) {
-    const sorted_row_keys = get_sorted_row_keys(row_dict);
-    const sorted_row_dict = new Map();
-    for (const row_key of sorted_row_keys) {
-        sorted_row_dict.set(row_key, row_dict.get(row_key));
-    }
-    return sorted_row_dict;
-}
-
-function reset_data() {
+function reset_data(): {
+    unread_dms_count: number;
+    is_dms_collapsed: boolean;
+    has_dms_post_filter: boolean;
+    has_visible_unreads: boolean;
+} {
     dms_dict = new Map();
     topics_dict = new Map();
     streams_dict = new Map();
@@ -478,7 +607,7 @@ function reset_data() {
             const stream_key = get_stream_key(stream_id);
             if (stream_unread_count > 0) {
                 update_stream_data(stream_id, stream_key, topic_dict);
-                if (!streams_dict.get(stream_key).is_hidden) {
+                if (!streams_dict.get(stream_key)!.is_hidden) {
                     has_topics_post_filter = true;
                 }
             } else {
@@ -499,7 +628,7 @@ function reset_data() {
     };
 }
 
-function show_empty_inbox_text(has_visible_unreads) {
+function show_empty_inbox_text(has_visible_unreads: boolean): void {
     if (!has_visible_unreads) {
         $("#inbox-list").css("border-width", 0);
         if (search_keyword) {
@@ -516,11 +645,16 @@ function show_empty_inbox_text(has_visible_unreads) {
     }
 }
 
-function filter_click_handler(event, dropdown, widget) {
+function filter_click_handler(
+    event: JQuery.TriggeredEvent,
+    dropdown: tippy.Instance,
+    widget: dropdown_widget.DropdownWidget,
+): void {
     event.preventDefault();
     event.stopPropagation();
 
     const filter_id = $(event.currentTarget).attr("data-unique-id");
+    assert(filter_id !== undefined);
     // We don't support multiple filters yet, so we clear existing and add the new filter.
     filters = new Set([filter_id]);
     save_data_to_ls();
@@ -529,7 +663,7 @@ function filter_click_handler(event, dropdown, widget) {
     update();
 }
 
-export function complete_rerender() {
+export function complete_rerender(): void {
     if (!is_visible()) {
         return;
     }
@@ -556,18 +690,19 @@ export function complete_rerender() {
         revive_current_focus();
     }, 0);
 
+    const first_filter = filters.values().next();
     filters_dropdown_widget = new dropdown_widget.DropdownWidget({
         ...views_util.COMMON_DROPDOWN_WIDGET_PARAMS,
         widget_name: "inbox-filter",
         item_click_callback: filter_click_handler,
         $events_container: $("#inbox-main"),
-        default_id: filters.values().next().value,
+        default_id: first_filter.done ? undefined : first_filter.value,
     });
     filters_dropdown_widget.setup();
 }
 
-export function search_and_update() {
-    const new_keyword = $("#inbox-search").val() || "";
+export function search_and_update(): void {
+    const new_keyword = $<HTMLInputElement>("input#inbox-search").val() ?? "";
     if (new_keyword === search_keyword) {
         return;
     }
@@ -577,7 +712,7 @@ export function search_and_update() {
     update();
 }
 
-function row_in_search_results(keyword, text) {
+function row_in_search_results(keyword: string, text: string): boolean {
     if (keyword === "") {
         return true;
     }
@@ -585,7 +720,7 @@ function row_in_search_results(keyword, text) {
     return search_words.every((word) => text.includes(word));
 }
 
-function filter_should_hide_dm_row({dm_key}) {
+function filter_should_hide_dm_row({dm_key}: {dm_key: string}): boolean {
     const recipients_string = people.get_recipients(dm_key);
     const text = recipients_string.toLowerCase();
 
@@ -596,9 +731,15 @@ function filter_should_hide_dm_row({dm_key}) {
     return false;
 }
 
-function filter_should_hide_stream_row({stream_id, topic}) {
+function filter_should_hide_stream_row({
+    stream_id,
+    topic,
+}: {
+    stream_id: number;
+    topic: string;
+}): boolean {
     const sub = sub_store.get(stream_id);
-    if (sub === undefined || !sub.subscribed) {
+    if (!sub?.subscribed) {
         return true;
     }
 
@@ -626,7 +767,7 @@ function filter_should_hide_stream_row({stream_id, topic}) {
     return false;
 }
 
-export function collapse_or_expand(container_id) {
+export function collapse_or_expand(container_id: string): void {
     let $toggle_icon;
     let $container;
     if (container_id === "inbox-dm-header") {
@@ -634,7 +775,7 @@ export function collapse_or_expand(container_id) {
         $container.children().toggleClass("collapsed_container");
         $toggle_icon = $("#inbox-dm-header .toggle-inbox-header-icon");
     } else {
-        const stream_id = container_id.slice(STREAM_HEADER_PREFIX.length);
+        const stream_id = Number(container_id.slice(STREAM_HEADER_PREFIX.length));
         $container = get_topics_container(stream_id);
         $container.children().toggleClass("collapsed_container");
         $toggle_icon = $(
@@ -652,35 +793,39 @@ export function collapse_or_expand(container_id) {
     save_data_to_ls();
 }
 
-function focus_current_id() {
+function focus_current_id(): void {
+    assert(current_focus_id !== undefined);
     $(`#${CSS.escape(current_focus_id)}`).trigger("focus");
 }
 
-function focus_inbox_search() {
+function focus_inbox_search(): void {
     current_focus_id = INBOX_SEARCH_ID;
     focus_current_id();
 }
 
-function is_list_focused() {
-    return ![INBOX_SEARCH_ID, INBOX_FILTERS_DROPDOWN_ID].includes(current_focus_id);
+function is_list_focused(): boolean {
+    return (
+        current_focus_id === undefined ||
+        ![INBOX_SEARCH_ID, INBOX_FILTERS_DROPDOWN_ID].includes(current_focus_id)
+    );
 }
 
-function get_all_rows() {
+function get_all_rows(): JQuery {
     return $(".inbox-header, .inbox-row").not(".hidden_by_filters, .collapsed_container");
 }
 
-function get_row_index($elt) {
+function get_row_index($elt: JQuery): number {
     const $all_rows = get_all_rows();
     const $row = $elt.closest(".inbox-row, .inbox-header");
     return $all_rows.index($row);
 }
 
-function focus_clicked_list_element($elt) {
+function focus_clicked_list_element($elt: JQuery): void {
     row_focus = get_row_index($elt);
     update_triggered_by_user = true;
 }
 
-function revive_current_focus() {
+function revive_current_focus(): void {
     if (is_list_focused()) {
         set_list_focus();
     } else {
@@ -688,7 +833,7 @@ function revive_current_focus() {
     }
 }
 
-function update_closed_compose_text($row, is_header_row) {
+function update_closed_compose_text($row: JQuery, is_header_row: boolean): void {
     // TODO: This fake "message" object is designed to allow using the
     // get_recipient_label helper inside compose_closed_ui. Surely
     // there's a more readable way to write this code.
@@ -708,66 +853,75 @@ function update_closed_compose_text($row, is_header_row) {
     } else {
         const $stream = $row.parent(".inbox-topic-container").prev(".inbox-header");
         message = {
-            stream_id: Number.parseInt($stream.attr("data-stream-id"), 10),
+            stream_id: Number($stream.attr("data-stream-id")),
             topic: $row.find(".inbox-topic-name a").text(),
         };
     }
     compose_closed_ui.update_reply_recipient_label(message);
 }
 
-export function get_focused_row_message() {
+export function get_focused_row_message(): {message?: Message} & (
+    | {msg_type: "private"; private_message_recipient?: string}
+    | {msg_type: "stream"; stream_id: number; topic?: string}
+    | {msg_type?: never}
+) {
     if (!is_list_focused()) {
         return {message: undefined};
     }
 
     const $all_rows = get_all_rows();
-    const $focused_row = $($all_rows.get(row_focus));
+    const focused_row = $all_rows.get(row_focus);
+    assert(focused_row !== undefined);
+    const $focused_row = $(focused_row);
     if (is_row_a_header($focused_row)) {
         const is_dm_header = $focused_row.attr("id") === "inbox-dm-header";
         if (is_dm_header) {
             return {message: undefined, msg_type: "private"};
         }
 
-        const stream_id = Number.parseInt($focused_row.attr("data-stream-id"), 10);
+        const stream_id = Number($focused_row.attr("data-stream-id"));
         compose_state.set_compose_recipient_id(stream_id);
         return {message: undefined, msg_type: "stream", stream_id};
     }
 
     const is_dm = $focused_row.parent("#inbox-direct-messages-container").length > 0;
-    const conversation_key = $focused_row.attr("id").slice(CONVERSATION_ID_PREFIX.length);
-    let row_info;
-    if (is_dm) {
-        row_info = dms_dict.get(conversation_key);
-    } else {
-        const $stream = $focused_row.parent(".inbox-topic-container").parent();
-        const stream_key = $stream.attr("id");
-        row_info = topics_dict.get(stream_key).get(conversation_key);
-    }
+    const conversation_key = $focused_row.attr("id")!.slice(CONVERSATION_ID_PREFIX.length);
 
-    const message = message_store.get(row_info.latest_msg_id);
-    // Since inbox is populated based on unread data which is part
-    // of /register request, it is possible that we don't have the
-    // actual message in our message_store. In that case, we return
-    // a fake message object.
-    if (message === undefined) {
-        if (is_dm) {
+    if (is_dm) {
+        const row_info = dms_dict.get(conversation_key);
+        assert(row_info !== undefined);
+        const message = message_store.get(row_info.latest_msg_id);
+        if (message === undefined) {
             const recipients = people.user_ids_string_to_emails_string(row_info.user_ids_string);
             return {
                 msg_type: "private",
                 private_message_recipient: recipients,
             };
         }
+        return {message};
+    }
+
+    const $stream = $focused_row.parent(".inbox-topic-container").parent();
+    const stream_key = $stream.attr("id");
+    assert(stream_key !== undefined);
+    const row_info = topics_dict.get(stream_key)!.get(conversation_key);
+    assert(row_info !== undefined);
+    const message = message_store.get(row_info.latest_msg_id);
+    // Since inbox is populated based on unread data which is part
+    // of /register request, it is possible that we don't have the
+    // actual message in our message_store. In that case, we return
+    // a fake message object.
+    if (message === undefined) {
         return {
             msg_type: "stream",
             stream_id: row_info.stream_id,
             topic: row_info.topic_name,
         };
     }
-
     return {message};
 }
 
-export function toggle_topic_visibility_policy() {
+export function toggle_topic_visibility_policy(): boolean {
     const inbox_message = get_focused_row_message();
     if (inbox_message.message !== undefined) {
         user_topics_ui.toggle_topic_visibility_policy(inbox_message.message);
@@ -782,11 +936,11 @@ export function toggle_topic_visibility_policy() {
     return false;
 }
 
-function is_row_a_header($row) {
+function is_row_a_header($row: JQuery): boolean {
     return $row.hasClass("inbox-header");
 }
 
-function set_list_focus(input_key) {
+function set_list_focus(input_key?: string): void {
     // This function is used for both revive_current_focus and
     // setting focus after modify col_focus and row_focus as per
     // hotkey pressed by user.
@@ -808,7 +962,9 @@ function set_list_focus(input_key) {
         row_focus = 0;
     }
 
-    const $row_to_focus = $($all_rows.get(row_focus));
+    const row_to_focus = $all_rows.get(row_focus);
+    assert(row_to_focus !== undefined);
+    const $row_to_focus = $(row_to_focus);
     // This includes a fake collapse button for `inbox-row` and a fake topic visibility
     // button for `inbox-header`. The fake buttons help simplify code here and
     // `$($cols_to_focus[col_focus]).trigger("focus");` at the end of this function.
@@ -827,18 +983,18 @@ function set_list_focus(input_key) {
 
     // Since header rows always have a collapse button, other rows have one less element to focus.
     if (col_focus === COLUMNS.COLLAPSE_BUTTON) {
-        if (!is_header_row && LEFT_NAVIGATION_KEYS.includes(input_key)) {
+        if (!is_header_row && input_key !== undefined && LEFT_NAVIGATION_KEYS.includes(input_key)) {
             // In `inbox-row` user pressed left on COLUMNS.RECIPIENT, so
             // go to the last column.
             col_focus = total_cols - 1;
         }
     } else if (!is_header_row && col_focus === COLUMNS.RECIPIENT) {
-        if (RIGHT_NAVIGATION_KEYS.includes(input_key)) {
+        if (input_key !== undefined && RIGHT_NAVIGATION_KEYS.includes(input_key)) {
             // In `inbox-row` user pressed right on COLUMNS.COLLAPSE_BUTTON.
             // Since `inbox-row` has no collapse button, user wants to go
             // to the unread count button.
             col_focus = COLUMNS.UNREAD_COUNT;
-        } else if (LEFT_NAVIGATION_KEYS.includes(input_key)) {
+        } else if (input_key !== undefined && LEFT_NAVIGATION_KEYS.includes(input_key)) {
             // In `inbox-row` user pressed left on COLUMNS.UNREAD_COUNT,
             // we move focus to COLUMNS.COLLAPSE_BUTTON so that moving
             // up or down to `inbox-header` keeps the entire row focused for the
@@ -853,7 +1009,7 @@ function set_list_focus(input_key) {
     } else if (is_header_row && col_focus === COLUMNS.TOPIC_VISIBILITY) {
         // `inbox-header` doesn't have a topic visibility indicator, so focus on
         // button around it instead.
-        if (LEFT_NAVIGATION_KEYS.includes(input_key)) {
+        if (input_key !== undefined && LEFT_NAVIGATION_KEYS.includes(input_key)) {
             col_focus = COLUMNS.UNREAD_COUNT;
         } else {
             col_focus = COLUMNS.ACTION_MENU;
@@ -863,22 +1019,23 @@ function set_list_focus(input_key) {
     $($cols_to_focus[col_focus]).trigger("focus");
 }
 
-function focus_filters_dropdown() {
+function focus_filters_dropdown(): void {
     current_focus_id = INBOX_FILTERS_DROPDOWN_ID;
     $(`#${CSS.escape(INBOX_FILTERS_DROPDOWN_ID)}`).trigger("focus");
 }
 
-function is_search_focused() {
+function is_search_focused(): boolean {
     return current_focus_id === INBOX_SEARCH_ID;
 }
 
-function is_filters_dropdown_focused() {
+function is_filters_dropdown_focused(): boolean {
     return current_focus_id === INBOX_FILTERS_DROPDOWN_ID;
 }
 
-function get_page_up_down_delta() {
+function get_page_up_down_delta(): number {
     const element_above = document.querySelector("#inbox-filters");
     const element_down = document.querySelector("#compose");
+    assert(element_above !== null && element_down !== null);
     const visible_top = element_above.getBoundingClientRect().bottom;
     const visible_bottom = element_down.getBoundingClientRect().top;
     // One usually wants PageDown to move what had been the bottom row
@@ -892,7 +1049,7 @@ function get_page_up_down_delta() {
     return delta;
 }
 
-function page_up_navigation() {
+function page_up_navigation(): void {
     const delta = get_page_up_down_delta();
     const scroll_element = document.documentElement;
     const new_scrollTop = scroll_element.scrollTop - delta;
@@ -903,13 +1060,13 @@ function page_up_navigation() {
     set_list_focus();
 }
 
-function page_down_navigation() {
+function page_down_navigation(): void {
     const delta = get_page_up_down_delta();
     const scroll_element = document.documentElement;
     const new_scrollTop = scroll_element.scrollTop + delta;
     const $all_rows = get_all_rows();
     const $last_row = $all_rows.last();
-    const last_row_bottom = $last_row.offset().top + $last_row.outerHeight();
+    const last_row_bottom = ($last_row.offset()?.top ?? 0) + ($last_row.outerHeight() ?? 0);
     // Move focus to last row if it is visible and we are at the bottom.
     if (last_row_bottom <= new_scrollTop) {
         row_focus = get_all_rows().length - 1;
@@ -918,11 +1075,12 @@ function page_down_navigation() {
     set_list_focus();
 }
 
-export function change_focused_element(input_key) {
+export function change_focused_element(input_key: string): boolean {
     if (is_search_focused()) {
-        const textInput = $(`#${CSS.escape(INBOX_SEARCH_ID)}`).get(0);
-        const start = textInput.selectionStart;
-        const end = textInput.selectionEnd;
+        const textInput = $<HTMLInputElement>(`input#${CSS.escape(INBOX_SEARCH_ID)}`).get(0);
+        assert(textInput !== undefined);
+        const start = textInput.selectionStart ?? 0;
+        const end = textInput.selectionEnd ?? 0;
         const text_length = textInput.value.length;
         let is_selected = false;
         if (end - start > 0) {
@@ -1021,7 +1179,7 @@ export function change_focused_element(input_key) {
     return false;
 }
 
-export function update() {
+export function update(): void {
     if (!is_visible()) {
         return;
     }
@@ -1034,7 +1192,7 @@ export function update() {
     const unread_streams_dict = unread_stream_message.topic_counts;
 
     let has_dms_post_filter = false;
-    const dm_keys_to_insert = [];
+    const dm_keys_to_insert: string[] = [];
     for (const [key, {count, latest_msg_id}] of unread_dms_dict) {
         if (count !== 0) {
             const old_dm_data = dms_dict.get(key);
@@ -1071,8 +1229,10 @@ export function update() {
         const stream_key = get_stream_key(stream_id);
         let stream_post_filter_unread_count = 0;
         if (stream_unread_count > 0) {
+            const stream_topics_data = topics_dict.get(stream_key);
+
             // Stream isn't rendered.
-            if (topics_dict.get(stream_key) === undefined) {
+            if (stream_topics_data === undefined) {
                 const is_stream_visible = insert_stream(stream_id, topic_dict);
                 if (is_stream_visible) {
                     has_topics_post_filter = true;
@@ -1080,19 +1240,19 @@ export function update() {
                 continue;
             }
 
-            const topic_keys_to_insert = [];
+            const topic_keys_to_insert: string[] = [];
             const new_stream_data = format_stream(stream_id);
             for (const [topic, {topic_count, latest_msg_id}] of topic_dict) {
                 const topic_key = get_topic_key(stream_id, topic);
                 if (topic_count) {
-                    const old_topic_data = topics_dict.get(stream_key).get(topic_key);
+                    const old_topic_data = stream_topics_data.get(topic_key);
                     const new_topic_data = format_topic(
                         stream_id,
                         topic,
                         topic_count,
                         latest_msg_id,
                     );
-                    topics_dict.get(stream_key).set(topic_key, new_topic_data);
+                    stream_topics_data.set(topic_key, new_topic_data);
                     rerender_topic_inbox_row_if_needed(
                         new_topic_data,
                         old_topic_data,
@@ -1105,16 +1265,17 @@ export function update() {
                 } else {
                     // Remove old topic data since it can act as false data for renamed / a new
                     // topic having the same name as old topic.
-                    topics_dict.get(stream_key).delete(topic_key);
+                    stream_topics_data.delete(topic_key);
                     get_row_from_conversation_key(topic_key).remove();
                 }
             }
             const old_stream_data = streams_dict.get(stream_key);
+            assert(old_stream_data !== undefined);
             new_stream_data.is_hidden = stream_post_filter_unread_count === 0;
             new_stream_data.unread_count = stream_post_filter_unread_count;
             streams_dict.set(stream_key, new_stream_data);
             rerender_stream_inbox_header_if_needed(new_stream_data, old_stream_data);
-            topics_dict.set(stream_key, get_sorted_row_dict(topics_dict.get(stream_key)));
+            topics_dict.set(stream_key, get_sorted_row_dict(stream_topics_data));
             insert_topics(topic_keys_to_insert, stream_key);
         } else {
             topics_dict.delete(stream_key);
@@ -1132,7 +1293,7 @@ export function update() {
     }
 }
 
-function get_focus_class_for_header() {
+function get_focus_class_for_header(): string {
     let focus_class = ".collapsible-button";
 
     switch (col_focus) {
@@ -1152,7 +1313,7 @@ function get_focus_class_for_header() {
     return focus_class;
 }
 
-function get_focus_class_for_row() {
+function get_focus_class_for_row(): string {
     let focus_class = ".inbox-left-part";
     switch (col_focus) {
         case COLUMNS.UNREAD_COUNT: {
@@ -1171,9 +1332,10 @@ function get_focus_class_for_row() {
     return focus_class;
 }
 
-function is_element_visible(element_position) {
+function is_element_visible(element_position: DOMRect): boolean {
     const element_above = document.querySelector("#inbox-filters");
     const element_down = document.querySelector("#compose");
+    assert(element_above !== null && element_down !== null);
     const visible_top = element_above.getBoundingClientRect().bottom;
     const visible_bottom = element_down.getBoundingClientRect().top;
 
@@ -1183,7 +1345,7 @@ function is_element_visible(element_position) {
     return false;
 }
 
-function center_focus_if_offscreen() {
+function center_focus_if_offscreen(): void {
     // Move focused to row to visible area so to avoid
     // it being under compose box or inbox filters.
     const $elt = $(".inbox-row:focus, .inbox-header:focus");
@@ -1201,7 +1363,7 @@ function center_focus_if_offscreen() {
     $elt[0].scrollIntoView({block: "center"});
 }
 
-function move_focus_to_visible_area() {
+function move_focus_to_visible_area(): void {
     // Focus on the row below inbox filters if the focused
     // row is not visible.
     if (!is_list_focused()) {
@@ -1229,18 +1391,20 @@ function move_focus_to_visible_area() {
     const inbox_center_x = (position.left + position.right) / 2;
     // We are aiming to get the first row if it is completely visible or the second row.
     const inbox_row_below_filters = position.bottom + INBOX_ROW_HEIGHT;
-    const $element_in_row = $(document.elementFromPoint(inbox_center_x, inbox_row_below_filters));
+    const element_in_row = document.elementFromPoint(inbox_center_x, inbox_row_below_filters);
+    assert(element_in_row !== null);
+    const $element_in_row = $(element_in_row);
 
     let $inbox_row = $element_in_row.closest(".inbox-row");
     if (!$inbox_row.length) {
         $inbox_row = $element_in_row.closest(".inbox-header");
     }
 
-    row_focus = $all_rows.index($inbox_row);
+    row_focus = $all_rows.index($inbox_row.get(0));
     revive_current_focus();
 }
 
-export function is_in_focus() {
+export function is_in_focus(): boolean {
     // Check if user is focused on
     // inbox
     return (
@@ -1254,7 +1418,7 @@ export function is_in_focus() {
     );
 }
 
-export function initialize() {
+export function initialize(): void {
     $(document).on(
         "scroll",
         _.throttle(() => {
@@ -1284,14 +1448,19 @@ export function initialize() {
         }
     });
 
-    $("body").on("click", "#inbox-list .inbox-header .collapsible-button", (e) => {
-        const $elt = $(e.currentTarget);
-        const container_id = $elt.parents(".inbox-header").attr("id");
-        col_focus = COLUMNS.COLLAPSE_BUTTON;
-        focus_clicked_list_element($elt);
-        collapse_or_expand(container_id);
-        e.stopPropagation();
-    });
+    $("body").on(
+        "click",
+        "#inbox-list .inbox-header .collapsible-button",
+        function (this: HTMLElement, e) {
+            const $elt = $(this);
+            const container_id = $elt.parents(".inbox-header").attr("id");
+            assert(container_id !== undefined);
+            col_focus = COLUMNS.COLLAPSE_BUTTON;
+            focus_clicked_list_element($elt);
+            collapse_or_expand(container_id);
+            e.stopPropagation();
+        },
+    );
 
     $("body").on("keydown", ".inbox-row", (e) => {
         if (e.metaKey || e.ctrlKey) {
@@ -1307,21 +1476,23 @@ export function initialize() {
         }
     });
 
-    $("body").on("click", "#inbox-list .inbox-left-part-wrapper", (e) => {
+    $("body").on("click", "#inbox-list .inbox-left-part-wrapper", function (this: HTMLElement, e) {
         if (e.metaKey || e.ctrlKey || e.shiftKey) {
             return;
         }
 
-        const $elt = $(e.currentTarget);
+        const $elt = $(this);
         col_focus = COLUMNS.RECIPIENT;
         focus_clicked_list_element($elt);
-        window.location.href = $elt.find("a").attr("href");
+        const href = $elt.find("a").attr("href");
+        assert(href !== undefined);
+        window.location.href = href;
     });
 
-    $("body").on("click", "#inbox-list .on_hover_dm_read", (e) => {
+    $("body").on("click", "#inbox-list .on_hover_dm_read", function (this: HTMLElement, e) {
         e.stopPropagation();
         e.preventDefault();
-        const $elt = $(e.currentTarget);
+        const $elt = $(this);
         col_focus = COLUMNS.UNREAD_COUNT;
         focus_clicked_list_element($elt);
         const user_ids_string = $elt.attr("data-user-ids-string");
@@ -1335,16 +1506,20 @@ export function initialize() {
         e.stopPropagation();
         e.preventDefault();
         const unread_dms_msg_ids = unread.get_msg_ids_for_private();
-        const unread_dms_messages = unread_dms_msg_ids.map((msg_id) => message_store.get(msg_id));
+        const unread_dms_messages = unread_dms_msg_ids.map((msg_id) => {
+            const message = message_store.get(msg_id);
+            assert(message !== undefined);
+            return message;
+        });
         unread_ops.notify_server_messages_read(unread_dms_messages);
         focus_inbox_search();
         update_triggered_by_user = true;
     });
 
-    $("body").on("click", "#inbox-list .on_hover_topic_read", (e) => {
+    $("body").on("click", "#inbox-list .on_hover_topic_read", function (this: HTMLElement, e) {
         e.stopPropagation();
         e.preventDefault();
-        const $elt = $(e.currentTarget);
+        const $elt = $(this);
         col_focus = COLUMNS.UNREAD_COUNT;
         focus_clicked_list_element($elt);
         const user_ids_string = $elt.attr("data-user-ids-string");
@@ -1353,7 +1528,7 @@ export function initialize() {
             unread_ops.mark_pm_as_read(user_ids_string);
             return;
         }
-        const stream_id = Number.parseInt($elt.attr("data-stream-id"), 10);
+        const stream_id = Number($elt.attr("data-stream-id"));
         const topic = $elt.attr("data-topic-name");
         if (topic) {
             unread_ops.mark_topic_as_read(stream_id, topic);
@@ -1374,40 +1549,56 @@ export function initialize() {
     });
 
     // Mute topic in a unmuted stream
-    $("body").on("click", "#inbox-list .stream_unmuted.on_hover_topic_mute", (e) => {
-        e.stopPropagation();
-        user_topics.set_visibility_policy_for_element(
-            $(e.target),
-            user_topics.all_visibility_policies.MUTED,
-        );
-    });
+    $("body").on(
+        "click",
+        "#inbox-list .stream_unmuted.on_hover_topic_mute",
+        function (this: HTMLElement, e) {
+            e.stopPropagation();
+            user_topics.set_visibility_policy_for_element(
+                $(this),
+                user_topics.all_visibility_policies.MUTED,
+            );
+        },
+    );
 
     // Unmute topic in a unmuted stream
-    $("body").on("click", "#inbox-list .stream_unmuted.on_hover_topic_unmute", (e) => {
-        e.stopPropagation();
-        user_topics.set_visibility_policy_for_element(
-            $(e.target),
-            user_topics.all_visibility_policies.INHERIT,
-        );
-    });
+    $("body").on(
+        "click",
+        "#inbox-list .stream_unmuted.on_hover_topic_unmute",
+        function (this: HTMLElement, e) {
+            e.stopPropagation();
+            user_topics.set_visibility_policy_for_element(
+                $(this),
+                user_topics.all_visibility_policies.INHERIT,
+            );
+        },
+    );
 
     // Unmute topic in a muted stream
-    $("body").on("click", "#inbox-list .stream_muted.on_hover_topic_unmute", (e) => {
-        e.stopPropagation();
-        user_topics.set_visibility_policy_for_element(
-            $(e.target),
-            user_topics.all_visibility_policies.UNMUTED,
-        );
-    });
+    $("body").on(
+        "click",
+        "#inbox-list .stream_muted.on_hover_topic_unmute",
+        function (this: HTMLElement, e) {
+            e.stopPropagation();
+            user_topics.set_visibility_policy_for_element(
+                $(this),
+                user_topics.all_visibility_policies.UNMUTED,
+            );
+        },
+    );
 
     // Mute topic in a muted stream
-    $("body").on("click", "#inbox-list .stream_muted.on_hover_topic_mute", (e) => {
-        e.stopPropagation();
-        user_topics.set_visibility_policy_for_element(
-            $(e.target),
-            user_topics.all_visibility_policies.INHERIT,
-        );
-    });
+    $("body").on(
+        "click",
+        "#inbox-list .stream_muted.on_hover_topic_mute",
+        function (this: HTMLElement, e) {
+            e.stopPropagation();
+            user_topics.set_visibility_policy_for_element(
+                $(this),
+                user_topics.all_visibility_policies.INHERIT,
+            );
+        },
+    );
 
     $(document).on("compose_canceled.zulip", () => {
         if (is_visible()) {
diff --git a/web/src/recent_view_ui.ts b/web/src/recent_view_ui.ts
index c62a4dde9c..055fe8272e 100644
--- a/web/src/recent_view_ui.ts
+++ b/web/src/recent_view_ui.ts
@@ -551,7 +551,7 @@ type ConversationContext = {
           topic: string;
           topic_url: string;
           mention_in_unread: boolean;
-          visibility_policy: number | boolean;
+          visibility_policy: number | false;
           all_visibility_policies: {
               INHERIT: number;
               MUTED: number;
diff --git a/web/src/user_topics.ts b/web/src/user_topics.ts
index 1a7840bfb4..637f47cf94 100644
--- a/web/src/user_topics.ts
+++ b/web/src/user_topics.ts
@@ -70,7 +70,7 @@ export function update_user_topics(
     }
 }
 
-export function get_topic_visibility_policy(stream_id: number, topic: string): number | boolean {
+export function get_topic_visibility_policy(stream_id: number, topic: string): number | false {
     if (stream_id === undefined) {
         return false;
     }