diff --git a/tools/test-js-with-node b/tools/test-js-with-node
index 06ed8a4971..ac76619121 100755
--- a/tools/test-js-with-node
+++ b/tools/test-js-with-node
@@ -101,7 +101,7 @@ EXEMPT_FILES = make_set(
         "web/src/inbox_ui.js",
         "web/src/inbox_util.js",
         "web/src/info_overlay.js",
-        "web/src/invite.js",
+        "web/src/invite.ts",
         "web/src/lightbox.js",
         "web/src/list_util.ts",
         "web/src/list_widget.ts",
diff --git a/web/src/hbs.d.ts b/web/src/hbs.d.ts
index fa21b755b4..35bc9a539c 100644
--- a/web/src/hbs.d.ts
+++ b/web/src/hbs.d.ts
@@ -1,4 +1,4 @@
 declare module "*.hbs" {
-    const render: (context: unknown) => string;
+    const render: (context?: unknown) => string;
     export = render;
 }
diff --git a/web/src/invite.js b/web/src/invite.ts
similarity index 78%
rename from web/src/invite.js
rename to web/src/invite.ts
index 7d5c9d7067..e9c1f6fe2b 100644
--- a/web/src/invite.js
+++ b/web/src/invite.ts
@@ -2,6 +2,7 @@ import autosize from "autosize";
 import ClipboardJS from "clipboard";
 import {add} from "date-fns";
 import $ from "jquery";
+import assert from "minimalistic-assert";
 
 import copy_invite_link from "../templates/copy_invite_link.hbs";
 import render_invitation_failed_error from "../templates/invitation_failed_error.hbs";
@@ -26,7 +27,7 @@ import * as util from "./util";
 let custom_expiration_time_input = 10;
 let custom_expiration_time_unit = "days";
 
-function reset_error_messages() {
+function reset_error_messages(): void {
     $("#dialog_error").hide().text("").removeClass(common.status_classes);
 
     if (page_params.development_environment) {
@@ -34,39 +35,52 @@ function reset_error_messages() {
     }
 }
 
-function get_common_invitation_data() {
-    const invite_as = Number.parseInt($("#invite_as").val(), 10);
-    let expires_in = $("#expires_in").val();
+function get_common_invitation_data(): {
+    csrfmiddlewaretoken: string;
+    invite_as: number;
+    stream_ids: string;
+    invite_expires_in_minutes: string;
+    invitee_emails?: string;
+} {
+    const invite_as = Number.parseInt(
+        $<HTMLSelectElement & {type: "select-one"}>("select:not([multiple])#invite_as").val()!,
+        10,
+    );
+    const raw_expires_in = $<HTMLSelectElement & {type: "select-one"}>(
+        "select:not([multiple])#expires_in",
+    ).val()!;
     // See settings_config.expires_in_values for why we do this conversion.
-    if (expires_in === "null") {
-        expires_in = JSON.stringify(null);
-    } else if (expires_in === "custom") {
-        expires_in = Number.parseFloat(get_expiration_time_in_minutes());
+    let expires_in: number | null;
+    if (raw_expires_in === "null") {
+        expires_in = null;
+    } else if (raw_expires_in === "custom") {
+        expires_in = get_expiration_time_in_minutes();
     } else {
-        expires_in = Number.parseFloat($("#expires_in").val());
+        expires_in = Number.parseFloat(raw_expires_in);
     }
 
-    let stream_ids = [];
+    let stream_ids: number[] = [];
     const default_stream_ids = stream_data.get_default_stream_ids();
     if (default_stream_ids.length !== 0 && $("#invite_select_default_streams").prop("checked")) {
         stream_ids = default_stream_ids;
     } else {
-        $("#invite-stream-checkboxes input:checked").each(function () {
-            const stream_id = Number.parseInt($(this).val(), 10);
+        $<HTMLInputElement>("#invite-stream-checkboxes input:checked").each(function () {
+            const stream_id = Number.parseInt($(this).val()!, 10);
             stream_ids.push(stream_id);
         });
     }
 
+    assert(csrf_token !== undefined);
     const data = {
         csrfmiddlewaretoken: csrf_token,
         invite_as,
         stream_ids: JSON.stringify(stream_ids),
-        invite_expires_in_minutes: expires_in,
+        invite_expires_in_minutes: JSON.stringify(expires_in),
     };
     return data;
 }
 
-function beforeSend() {
+function beforeSend(): void {
     reset_error_messages();
     // TODO: You could alternatively parse the textarea here, and return errors to
     // the user if they don't match certain constraints (i.e. not real email addresses,
@@ -76,16 +90,18 @@ function beforeSend() {
     const loading_text = $("#invite-user-modal .dialog_submit_button").data("loading-text");
     $("#invite-user-modal .dialog_submit_button").text(loading_text);
     $("#invite-user-modal .dialog_submit_button").prop("disabled", true);
-    return true;
 }
 
-function submit_invitation_form() {
+function submit_invitation_form(): void {
+    const $expires_in = $<HTMLSelectElement & {type: "select-one"}>(
+        "select:not([multiple])#expires_in",
+    );
     const $invite_status = $("#dialog_error");
-    const $invitee_emails = $("#invitee_emails");
+    const $invitee_emails = $<HTMLTextAreaElement>("textarea#invitee_emails");
     const data = get_common_invitation_data();
-    data.invitee_emails = $("#invitee_emails").val();
+    data.invitee_emails = $invitee_emails.val()!;
 
-    channel.post({
+    void channel.post({
         url: "/json/invites",
         data,
         beforeSend,
@@ -101,14 +117,14 @@ function submit_invitation_form() {
                 $("#dev_env_msg").html(rendered_email_msg).addClass("alert-info").show();
             }
 
-            if ($("#expires_in").val() === "custom") {
+            if ($expires_in.val() === "custom") {
                 // Hide the custom inputs if the custom input is set
                 // to one of the dropdown's standard options.
                 const time_in_minutes = get_expiration_time_in_minutes();
                 for (const option of Object.values(settings_config.expires_in_values)) {
                     if (option.value === time_in_minutes) {
                         $("#custom-invite-expiration-time").hide();
-                        $("#expires_in").val(time_in_minutes);
+                        $expires_in.val(time_in_minutes);
                         return;
                     }
                 }
@@ -153,16 +169,16 @@ function submit_invitation_form() {
             $("#invite-user-modal .dialog_submit_button").text($t({defaultMessage: "Invite"}));
             $("#invite-user-modal .dialog_submit_button").prop("disabled", false);
             $("#invite-user-modal .dialog_exit_button").prop("disabled", false);
-            $("#invitee_emails").trigger("focus");
+            $<HTMLTextAreaElement>("textarea#invitee_emails").trigger("focus");
             scroll_util.get_scroll_element($("#invite-user-modal"))[0].scrollTop = 0;
         },
     });
 }
 
-function generate_multiuse_invite() {
+function generate_multiuse_invite(): void {
     const $invite_status = $("#dialog_error");
     const data = get_common_invitation_data();
-    channel.post({
+    void channel.post({
         url: "/json/invites/multiuse",
         data,
         beforeSend,
@@ -185,14 +201,13 @@ function generate_multiuse_invite() {
     });
 }
 
-export function get_invite_streams() {
+export function get_invite_streams(): stream_data.InviteStreamData[] {
     const streams = stream_data.get_invite_stream_data();
     streams.sort((a, b) => util.strcmp(a.name, b.name));
     return streams;
 }
 
-function valid_to(expires_in) {
-    const time_valid = Number.parseFloat(expires_in);
+function valid_to(time_valid: number): string {
     if (!time_valid) {
         return $t({defaultMessage: "Never expires"});
     }
@@ -205,7 +220,7 @@ function valid_to(expires_in) {
     return $t({defaultMessage: "Expires on {date} at {time}"}, {date, time});
 }
 
-function get_expiration_time_in_minutes() {
+function get_expiration_time_in_minutes(): number {
     switch (custom_expiration_time_unit) {
         case "hours":
             return custom_expiration_time_input * 60;
@@ -218,27 +233,35 @@ function get_expiration_time_in_minutes() {
     }
 }
 
-function set_expires_on_text() {
-    if ($("#expires_in").val() === "custom") {
+function set_expires_on_text(): void {
+    const $expires_in = $<HTMLSelectElement & {type: "select-one"}>(
+        "select:not([multiple])#expires_in",
+    );
+    if ($expires_in.val() === "custom") {
         $("#expires_on").hide();
         $("#custom_expires_on").text(valid_to(get_expiration_time_in_minutes()));
     } else {
         $("#expires_on").show();
-        $("#expires_on").text(valid_to($("#expires_in").val()));
+        $("#expires_on").text(valid_to(Number.parseFloat($expires_in.val()!)));
     }
 }
 
-function set_custom_time_inputs_visibility() {
-    if ($("#expires_in").val() === "custom") {
+function set_custom_time_inputs_visibility(): void {
+    const $expires_in = $<HTMLSelectElement & {type: "select-one"}>(
+        "select:not([multiple])#expires_in",
+    );
+    if ($expires_in.val() === "custom") {
         $("#custom-expiration-time-input").val(custom_expiration_time_input);
-        $("#custom-expiration-time-unit").val(custom_expiration_time_unit);
+        $<HTMLSelectElement & {type: "select-one"}>(
+            "select:not([multiple])#custom-expiration-time-unit",
+        ).val(custom_expiration_time_unit);
         $("#custom-invite-expiration-time").show();
     } else {
         $("#custom-invite-expiration-time").hide();
     }
 }
 
-function set_streams_to_join_list_visibility() {
+function set_streams_to_join_list_visibility(): void {
     const default_streams_selected = $("#invite_select_default_streams").prop("checked");
     if (default_streams_selected) {
         $("#streams_to_add .invite-stream-controls").hide();
@@ -249,7 +272,7 @@ function set_streams_to_join_list_visibility() {
     }
 }
 
-function open_invite_user_modal(e) {
+function open_invite_user_modal(e: JQuery.ClickEvent<Document, undefined>): void {
     e.stopPropagation();
     e.preventDefault();
 
@@ -269,7 +292,12 @@ function open_invite_user_modal(e) {
         user_has_email_set: !settings_data.user_email_not_configured(),
     });
 
-    function invite_user_modal_post_render() {
+    function invite_user_modal_post_render(): void {
+        const $expires_in = $<HTMLSelectElement & {type: "select-one"}>(
+            "select:not([multiple])#expires_in",
+        );
+        const $invitee_emails = $<HTMLTextAreaElement>("textarea#invitee_emails");
+
         $("#invite-user-modal .dialog_submit_button").prop("disabled", true);
         $("#email_invite_radio").prop("checked", true);
 
@@ -281,16 +309,16 @@ function open_invite_user_modal(e) {
 
         const user_has_email_set = !settings_data.user_email_not_configured();
 
-        autosize($("#invitee_emails").trigger("focus"));
+        autosize($invitee_emails.trigger("focus"));
 
         set_custom_time_inputs_visibility();
         set_expires_on_text();
         set_streams_to_join_list_visibility();
 
-        function toggle_invite_submit_button() {
+        function toggle_invite_submit_button(): void {
             $("#invite-user-modal .dialog_submit_button").prop(
                 "disabled",
-                $("#invitee_emails").val().trim() === "" &&
+                $invitee_emails.val()!.trim() === "" &&
                     !$("#generate_multiuse_invite_radio").is(":checked"),
             );
         }
@@ -323,12 +351,12 @@ function open_invite_user_modal(e) {
             reset_error_messages();
         });
 
-        $("#expires_in").on("change", () => {
+        $expires_in.on("change", () => {
             set_custom_time_inputs_visibility();
             set_expires_on_text();
         });
 
-        $("#expires_on").text(valid_to($("#expires_in").val()));
+        $("#expires_on").text(valid_to(Number.parseFloat($expires_in.val()!)));
 
         $("#custom-expiration-time-input").on("keydown", (e) => {
             if (e.key === "Enter") {
@@ -338,8 +366,12 @@ function open_invite_user_modal(e) {
         });
 
         $(".custom-expiration-time").on("change", () => {
-            custom_expiration_time_input = $("#custom-expiration-time-input").val();
-            custom_expiration_time_unit = $("#custom-expiration-time-unit").val();
+            custom_expiration_time_input = Number.parseFloat(
+                $<HTMLInputElement>("#custom-expiration-time-input").val()!,
+            );
+            custom_expiration_time_unit = $<HTMLSelectElement & {type: "select-one"}>(
+                "select:not([multiple])#custom-expiration-time-unit",
+            ).val()!;
             $("#custom_expires_on").text(valid_to(get_expiration_time_in_minutes()));
         });
 
@@ -371,7 +403,7 @@ function open_invite_user_modal(e) {
         }
     }
 
-    function invite_users() {
+    function invite_users(): void {
         const is_generate_invite_link = $("#generate_multiuse_invite_radio").prop("checked");
         if (is_generate_invite_link) {
             generate_multiuse_invite();
@@ -391,6 +423,6 @@ function open_invite_user_modal(e) {
     });
 }
 
-export function initialize() {
+export function initialize(): void {
     $(document).on("click", ".invite-user-link", open_invite_user_modal);
 }
diff --git a/web/src/page_params.ts b/web/src/page_params.ts
index b116bb992d..86f2ccaa2c 100644
--- a/web/src/page_params.ts
+++ b/web/src/page_params.ts
@@ -15,6 +15,7 @@ export const page_params: {
     login_page: string;
     delivery_email: string;
     is_admin: boolean;
+    is_billing_admin: boolean;
     is_bot: boolean;
     is_guest: boolean;
     is_moderator: boolean;
diff --git a/web/src/stream_data.ts b/web/src/stream_data.ts
index e0ce1a9f9e..44b4e9849e 100644
--- a/web/src/stream_data.ts
+++ b/web/src/stream_data.ts
@@ -33,7 +33,7 @@ type ApiGenericStreamSubscription =
     | ApiStreamSubscription
     | (Stream & {stream_weekly_traffic: number | null; subscribers: number[]});
 
-type InviteStreamData = {
+export type InviteStreamData = {
     name: string;
     stream_id: number;
     invite_only: boolean;