diff --git a/tools/test-js-with-node b/tools/test-js-with-node
index 38ff713a4f..3960b08295 100755
--- a/tools/test-js-with-node
+++ b/tools/test-js-with-node
@@ -168,7 +168,7 @@ EXEMPT_FILES = make_set(
         "web/src/plotly.js.d.ts",
         "web/src/pm_list.ts",
         "web/src/pm_list_dom.ts",
-        "web/src/poll_modal.js",
+        "web/src/poll_modal.ts",
         "web/src/poll_widget.ts",
         "web/src/popover_menus.ts",
         "web/src/popover_menus_data.js",
diff --git a/web/src/poll_modal.js b/web/src/poll_modal.ts
similarity index 68%
rename from web/src/poll_modal.js
rename to web/src/poll_modal.ts
index 316535f25c..5ddc243bca 100644
--- a/web/src/poll_modal.js
+++ b/web/src/poll_modal.ts
@@ -1,15 +1,15 @@
 import $ from "jquery";
-import {Sortable} from "sortablejs";
+import SortableJS from "sortablejs";
 
 import render_poll_modal_option from "../templates/poll_modal_option.hbs";
 
-function create_option_row($last_option_row_input) {
+function create_option_row($last_option_row_input: JQuery): void {
     const row = render_poll_modal_option();
     const $row_container = $last_option_row_input.closest(".simplebar-content");
     $row_container.append(row);
 }
 
-function add_option_row(e) {
+function add_option_row(e: JQuery.TriggeredEvent): void {
     // if the option triggering the input event e is not the last,
     // that is, its next sibling has the class `option-row`, we
     // do not add a new option row and return from this function
@@ -21,20 +21,20 @@ function add_option_row(e) {
     create_option_row($(e.target));
 }
 
-function delete_option_row(e) {
+function delete_option_row(e: JQuery.ClickEvent): void {
     const $row = $(e.target).closest(".option-row");
     $row.remove();
 }
 
-export function poll_options_setup() {
+export function poll_options_setup(): void {
     const $poll_options_list = $("#add-poll-form .poll-options-list");
     const $submit_button = $("#add-poll-modal .dialog_submit_button");
-    const $question_input = $("#add-poll-form #poll-question-input");
+    const $question_input = $<HTMLInputElement>("#add-poll-form input#poll-question-input");
 
     // Disable the submit button if the question is empty.
     $submit_button.prop("disabled", true);
     $question_input.on("input", () => {
-        if ($question_input.val().trim() !== "") {
+        if ($question_input.val()!.trim() !== "") {
             $submit_button.prop("disabled", false);
         } else {
             $submit_button.prop("disabled", true);
@@ -46,8 +46,10 @@ export function poll_options_setup() {
 
     // setTimeout is needed to here to give time for simplebar to initialise
     setTimeout(() => {
-        Sortable.create($("#add-poll-form .poll-options-list .simplebar-content")[0], {
-            onUpdate() {},
+        SortableJS.create($("#add-poll-form .poll-options-list .simplebar-content")[0], {
+            onUpdate() {
+                // Do nothing on drag; the order is only processed on submission.
+            },
             // We don't want the last (empty) row to be draggable, as a new row
             // is added on input event of the last row.
             filter: "input, .option-row:last-child",
@@ -56,11 +58,11 @@ export function poll_options_setup() {
     }, 0);
 }
 
-export function frame_poll_message_content() {
-    const question = $("#poll-question-input").val().trim();
-    const options = $(".poll-option-input")
+export function frame_poll_message_content(): string {
+    const question = $<HTMLInputElement>("input#poll-question-input").val()!.trim();
+    const options = $<HTMLInputElement>("input.poll-option-input")
         .map(function () {
-            return $(this).val().trim();
+            return $(this).val()!.trim();
         })
         .toArray()
         .filter(Boolean);