diff --git a/web_src/js/components/DiffCommitSelector.vue b/web_src/js/components/DiffCommitSelector.vue
index b95e18796c6..c78531cf9f3 100644
--- a/web_src/js/components/DiffCommitSelector.vue
+++ b/web_src/js/components/DiffCommitSelector.vue
@@ -142,11 +142,11 @@ export default {
       Object.assign(this.locale, results.locale);
     },
     showAllChanges() {
-      window.location = `${this.issueLink}/files${this.queryParams}`;
+      window.location.assign(`${this.issueLink}/files${this.queryParams}`);
     },
     /** Called when user clicks on since last review */
     changesSinceLastReviewClick() {
-      window.location = `${this.issueLink}/files/${this.lastReviewCommitSha}..${this.commits.at(-1).id}${this.queryParams}`;
+      window.location.assign(`${this.issueLink}/files/${this.lastReviewCommitSha}..${this.commits.at(-1).id}${this.queryParams}`);
     },
     /** Clicking on a single commit opens this specific commit */
     commitClicked(commitId, newWindow = false) {
@@ -154,7 +154,7 @@ export default {
       if (newWindow) {
         window.open(url);
       } else {
-        window.location = url;
+        window.location.assign(url);
       }
     },
     /**
@@ -176,14 +176,14 @@ export default {
           const lastCommitIdx = this.commits.findLastIndex((x) => x.selected);
           if (lastCommitIdx === this.commits.length - 1) {
             // user selected all commits - just show the normal diff page
-            window.location = `${this.issueLink}/files${this.queryParams}`;
+            window.location.assign(`${this.issueLink}/files${this.queryParams}`);
           } else {
-            window.location = `${this.issueLink}/files/${this.commits[lastCommitIdx].id}${this.queryParams}`;
+            window.location.assign(`${this.issueLink}/files/${this.commits[lastCommitIdx].id}${this.queryParams}`);
           }
         } else {
           const start = this.commits[this.commits.findIndex((x) => x.selected) - 1].id;
           const end = this.commits.findLast((x) => x.selected).id;
-          window.location = `${this.issueLink}/files/${start}..${end}${this.queryParams}`;
+          window.location.assign(`${this.issueLink}/files/${start}..${end}${this.queryParams}`);
         }
       }
     },
diff --git a/web_src/js/features/repo-issue.ts b/web_src/js/features/repo-issue.ts
index 5d5e3568b92..520f2081b0b 100644
--- a/web_src/js/features/repo-issue.ts
+++ b/web_src/js/features/repo-issue.ts
@@ -97,7 +97,7 @@ function excludeLabel(item) {
   const regStr = `labels=((?:-?[0-9]+%2c)*)(${id})((?:%2c-?[0-9]+)*)&`;
   const newStr = 'labels=$1-$2$3&';
 
-  window.location = href.replace(new RegExp(regStr), newStr);
+  window.location.assign(href.replace(new RegExp(regStr), newStr));
 }
 
 export function initRepoIssueSidebarList() {
diff --git a/web_src/js/utils/dom.ts b/web_src/js/utils/dom.ts
index 0e0830c9540..a6e0fe28543 100644
--- a/web_src/js/utils/dom.ts
+++ b/web_src/js/utils/dom.ts
@@ -92,7 +92,7 @@ export function onDomReady(cb: () => Promisable<void>) {
 
 // checks whether an element is owned by the current document, and whether it is a document fragment or element node
 // if it is, it means it is a "normal" element managed by us, which can be modified safely.
-export function isDocumentFragmentOrElementNode(el: Element) {
+export function isDocumentFragmentOrElementNode(el: Element | Node) {
   try {
     return el.ownerDocument === document && el.nodeType === Node.ELEMENT_NODE || el.nodeType === Node.DOCUMENT_FRAGMENT_NODE;
   } catch {
diff --git a/web_src/js/vendor/jquery.are-you-sure.ts b/web_src/js/vendor/jquery.are-you-sure.ts
index e7bb203c5a9..858f9871b8b 100644
--- a/web_src/js/vendor/jquery.are-you-sure.ts
+++ b/web_src/js/vendor/jquery.are-you-sure.ts
@@ -1,3 +1,4 @@
+// @ts-nocheck
 // Fork of the upstream module. The only changes are:
 // * use export to make it work with ES6 modules.
 // * the addition of `const` to make it strict mode compatible.
diff --git a/web_src/js/webcomponents/absolute-date.ts b/web_src/js/webcomponents/absolute-date.ts
index 6a053c6a55c..8eb1c3e37ea 100644
--- a/web_src/js/webcomponents/absolute-date.ts
+++ b/web_src/js/webcomponents/absolute-date.ts
@@ -26,7 +26,7 @@ window.customElements.define('absolute-date', class extends HTMLElement {
     this.shadowRoot.textContent = toAbsoluteLocaleDate(this.getAttribute('date'), lang, opt);
   };
 
-  attributeChangedCallback(_name, oldValue, newValue) {
+  attributeChangedCallback(_name: string, oldValue: string | null, newValue: string | null) {
     if (!this.initialized || oldValue === newValue) return;
     this.update();
   }
diff --git a/web_src/js/webcomponents/origin-url.test.ts b/web_src/js/webcomponents/origin-url.test.ts
index 4082e53aea9..19cc467d7df 100644
--- a/web_src/js/webcomponents/origin-url.test.ts
+++ b/web_src/js/webcomponents/origin-url.test.ts
@@ -1,9 +1,9 @@
 import {toOriginUrl} from './origin-url.ts';
 
 test('toOriginUrl', () => {
-  const oldLocation = window.location;
+  const oldLocation = String(window.location);
   for (const origin of ['https://example.com', 'https://example.com:3000']) {
-    window.location = new URL(`${origin}/`);
+    window.location.assign(`${origin}/`);
     expect(toOriginUrl('/')).toEqual(`${origin}/`);
     expect(toOriginUrl('/org/repo.git')).toEqual(`${origin}/org/repo.git`);
     expect(toOriginUrl('https://another.com')).toEqual(`${origin}/`);
@@ -13,5 +13,5 @@ test('toOriginUrl', () => {
     expect(toOriginUrl('https://another.com:4000/')).toEqual(`${origin}/`);
     expect(toOriginUrl('https://another.com:4000/org/repo.git')).toEqual(`${origin}/org/repo.git`);
   }
-  window.location = oldLocation;
+  window.location.assign(oldLocation);
 });
diff --git a/web_src/js/webcomponents/origin-url.ts b/web_src/js/webcomponents/origin-url.ts
index 09aa77f2c0f..d407fe0dff7 100644
--- a/web_src/js/webcomponents/origin-url.ts
+++ b/web_src/js/webcomponents/origin-url.ts
@@ -1,7 +1,7 @@
 // Convert an absolute or relative URL to an absolute URL with the current origin. It only
 // processes absolute HTTP/HTTPS URLs or relative URLs like '/xxx' or '//host/xxx'.
 // NOTE: Keep this function in sync with clone_script.tmpl
-export function toOriginUrl(urlStr) {
+export function toOriginUrl(urlStr: string) {
   try {
     if (urlStr.startsWith('http://') || urlStr.startsWith('https://') || urlStr.startsWith('/')) {
       const {origin, protocol, hostname, port} = window.location;
diff --git a/web_src/js/webcomponents/overflow-menu.ts b/web_src/js/webcomponents/overflow-menu.ts
index 2efeb9222b0..777d7dc65dd 100644
--- a/web_src/js/webcomponents/overflow-menu.ts
+++ b/web_src/js/webcomponents/overflow-menu.ts
@@ -4,6 +4,14 @@ import {isDocumentFragmentOrElementNode} from '../utils/dom.ts';
 import octiconKebabHorizontal from '../../../public/assets/img/svg/octicon-kebab-horizontal.svg';
 
 window.customElements.define('overflow-menu', class extends HTMLElement {
+  tippyContent: HTMLDivElement;
+  tippyItems: Array<HTMLElement>;
+  button: HTMLButtonElement;
+  menuItemsEl: HTMLElement;
+  resizeObserver: ResizeObserver;
+  mutationObserver: MutationObserver;
+  lastWidth: number;
+
   updateItems = throttle(100, () => { // eslint-disable-line unicorn/consistent-function-scoping -- https://github.com/sindresorhus/eslint-plugin-unicorn/issues/2088
     if (!this.tippyContent) {
       const div = document.createElement('div');
@@ -11,7 +19,7 @@ window.customElements.define('overflow-menu', class extends HTMLElement {
       div.tabIndex = -1; // for initial focus, programmatic focus only
       div.addEventListener('keydown', (e) => {
         if (e.key === 'Tab') {
-          const items = this.tippyContent.querySelectorAll('[role="menuitem"]');
+          const items = this.tippyContent.querySelectorAll<HTMLElement>('[role="menuitem"]');
           if (e.shiftKey) {
             if (document.activeElement === items[0]) {
               e.preventDefault();
@@ -32,27 +40,27 @@ window.customElements.define('overflow-menu', class extends HTMLElement {
           if (document.activeElement?.matches('[role="menuitem"]')) {
             e.preventDefault();
             e.stopPropagation();
-            document.activeElement.click();
+            (document.activeElement as HTMLElement).click();
           }
         } else if (e.key === 'ArrowDown') {
           if (document.activeElement?.matches('.tippy-target')) {
             e.preventDefault();
             e.stopPropagation();
-            document.activeElement.querySelector('[role="menuitem"]:first-of-type').focus();
+            document.activeElement.querySelector<HTMLElement>('[role="menuitem"]:first-of-type').focus();
           } else if (document.activeElement?.matches('[role="menuitem"]')) {
             e.preventDefault();
             e.stopPropagation();
-            document.activeElement.nextElementSibling?.focus();
+            (document.activeElement.nextElementSibling as HTMLElement)?.focus();
           }
         } else if (e.key === 'ArrowUp') {
           if (document.activeElement?.matches('.tippy-target')) {
             e.preventDefault();
             e.stopPropagation();
-            document.activeElement.querySelector('[role="menuitem"]:last-of-type').focus();
+            document.activeElement.querySelector<HTMLElement>('[role="menuitem"]:last-of-type').focus();
           } else if (document.activeElement?.matches('[role="menuitem"]')) {
             e.preventDefault();
             e.stopPropagation();
-            document.activeElement.previousElementSibling?.focus();
+            (document.activeElement.previousElementSibling as HTMLElement)?.focus();
           }
         }
       });
@@ -60,8 +68,8 @@ window.customElements.define('overflow-menu', class extends HTMLElement {
       this.tippyContent = div;
     }
 
-    const itemFlexSpace = this.menuItemsEl.querySelector('.item-flex-space');
-    const itemOverFlowMenuButton = this.querySelector('.overflow-menu-button');
+    const itemFlexSpace = this.menuItemsEl.querySelector<HTMLSpanElement>('.item-flex-space');
+    const itemOverFlowMenuButton = this.querySelector<HTMLButtonElement>('.overflow-menu-button');
 
     // move items in tippy back into the menu items for subsequent measurement
     for (const item of this.tippyItems || []) {
@@ -78,7 +86,7 @@ window.customElements.define('overflow-menu', class extends HTMLElement {
     itemOverFlowMenuButton?.style.setProperty('display', 'none', 'important');
     this.tippyItems = [];
     const menuRight = this.offsetLeft + this.offsetWidth;
-    const menuItems = this.menuItemsEl.querySelectorAll('.item, .item-flex-space');
+    const menuItems = this.menuItemsEl.querySelectorAll<HTMLElement>('.item, .item-flex-space');
     let afterFlexSpace = false;
     for (const item of menuItems) {
       if (item.classList.contains('item-flex-space')) {
@@ -189,14 +197,14 @@ window.customElements.define('overflow-menu', class extends HTMLElement {
     // template rendering, wait for its addition.
     // The eslint rule is not sophisticated enough or aware of this problem, see
     // https://github.com/43081j/eslint-plugin-wc/pull/130
-    const menuItemsEl = this.querySelector('.overflow-menu-items'); // eslint-disable-line wc/no-child-traversal-in-connectedcallback
+    const menuItemsEl = this.querySelector<HTMLElement>('.overflow-menu-items'); // eslint-disable-line wc/no-child-traversal-in-connectedcallback
     if (menuItemsEl) {
       this.menuItemsEl = menuItemsEl;
       this.init();
     } else {
       this.mutationObserver = new MutationObserver((mutations) => {
         for (const mutation of mutations) {
-          for (const node of mutation.addedNodes) {
+          for (const node of mutation.addedNodes as NodeListOf<HTMLElement>) {
             if (!isDocumentFragmentOrElementNode(node)) continue;
             if (node.classList.contains('overflow-menu-items')) {
               this.menuItemsEl = node;
diff --git a/web_src/js/webcomponents/polyfills.ts b/web_src/js/webcomponents/polyfills.ts
index 38f50fa02f5..4a84ee9562b 100644
--- a/web_src/js/webcomponents/polyfills.ts
+++ b/web_src/js/webcomponents/polyfills.ts
@@ -4,10 +4,11 @@ try {
   new Intl.NumberFormat('en', {style: 'unit', unit: 'minute'}).format(1);
 } catch {
   const intlNumberFormat = Intl.NumberFormat;
-  Intl.NumberFormat = function(locales, options) {
+  // @ts-expect-error - polyfill is incomplete
+  Intl.NumberFormat = function(locales: string | string[], options: Intl.NumberFormatOptions) {
     if (options.style === 'unit') {
       return {
-        format(value) {
+        format(value: number | bigint | string) {
           return ` ${value} ${options.unit}`;
         },
       };