diff --git a/.gitignore b/.gitignore
index 4802aa1..e19716d 100644
--- a/.gitignore
+++ b/.gitignore
@@ -11,4 +11,6 @@ node_modules/
 out/
 pnpm-debug.log
 tmp/
+types/
 *.log
+*.tgz
diff --git a/README.md b/README.md
index f69537d..253cf77 100644
--- a/README.md
+++ b/README.md
@@ -30,13 +30,14 @@ import TestPageOpener from 'test-page-opener'
 describe('TestPageOpener', () => {
   let opener
 
-  beforeAll(async () => opener = await TestPageOpener.create('/basedir/'))
+  beforeAll(async () => {opener = await TestPageOpener.create('/basedir/')})
   afterEach(() => opener.closeAll())
 
   test('loads page with module successfully', async () => {
     const { document } = await opener.open('path/to/index.html')
     const appElem = document.querySelector('#app')
 
+    expect(appElem).not.toBeNull()
     expect(appElem.textContent).toContain('Hello, World!')
   })
 })
diff --git a/ci/vitest.config.browser.js b/ci/vitest.config.browser.js
index 923c7b7..72ff124 100644
--- a/ci/vitest.config.browser.js
+++ b/ci/vitest.config.browser.js
@@ -1,5 +1,6 @@
+// @ts-nocheck
 import { defineConfig, mergeConfig } from 'vitest/config'
-import baseConfig from './vitest.config'
+import baseConfig from './vitest.config.js'
 
 export default mergeConfig(baseConfig, defineConfig({
   test: {
diff --git a/ci/vitest.config.js b/ci/vitest.config.js
index 1c775e6..b7a186a 100644
--- a/ci/vitest.config.js
+++ b/ci/vitest.config.js
@@ -1,5 +1,6 @@
+// @ts-nocheck
 import { defineConfig, mergeConfig } from 'vitest/config'
-import viteConfig from '../vite.config'
+import viteConfig from '../vite.config.js'
 
 export default mergeConfig(viteConfig, defineConfig({
   test: {
diff --git a/index.js b/index.js
index cc9c64f..880e530 100644
--- a/index.js
+++ b/index.js
@@ -21,13 +21,14 @@ import { OpenedPage } from './lib/types.js'
  * describe('TestPageOpener', () => {
  *   let opener
  *
- *   beforeAll(async () => opener = await TestPageOpener.create('/basedir/'))
+ *   beforeAll(async () => {opener = await TestPageOpener.create('/basedir/')})
  *   afterEach(() => opener.closeAll())
  *
  *   test('loads page with module successfully', async () => {
  *     const { document } = await opener.open('path/to/index.html')
  *     const appElem = document.querySelector('#app')
  *
+ *     expect(appElem).not.toBeNull()
  *     expect(appElem.textContent).toContain('Hello, World!')
  *   })
  * })
@@ -38,6 +39,7 @@ export default class TestPageOpener {
 
   #basePath
   #impl
+  /** @type {OpenedPage[]} */
   #opened
 
   /**
@@ -69,12 +71,13 @@ export default class TestPageOpener {
    *
    * ```js
    * let opener
-   * beforeAll(async () => opener = await TestPageOpener.create('/basedir/'))
+   * beforeAll(async () => {opener = await TestPageOpener.create('/basedir/')})
    * ```
    * @param {string} basePath - base path of the application under test; must
    *   start with '/' and end with '/'
-   * @returns {TestPageOpener} - a new TestPageOpener initialized to open pages
-   *   in the current test environment, either via Jsdom or the browser
+   * @returns {Promise<TestPageOpener>} - a new TestPageOpener initialized to
+   *   open pages in the current test environment, either via jsdom or the
+   *   browser
    */
   static async create(basePath) {
     const impl = globalThis.window ?
diff --git a/jsconfig.json b/jsconfig.json
new file mode 100644
index 0000000..5367b8a
--- /dev/null
+++ b/jsconfig.json
@@ -0,0 +1,10 @@
+{
+  "compilerOptions": {
+    "checkJs": true,
+    "module": "nodenext",
+    "strict": true,
+    "strictNullChecks": false,
+    "noImplicitAny": false
+  },
+  "exclude": ["node_modules"]
+}
diff --git a/jsdoc.json b/jsdoc.json
index b48e5f8..0361ec2 100644
--- a/jsdoc.json
+++ b/jsdoc.json
@@ -1,5 +1,7 @@
 {
-  "plugins": [ "plugins/markdown" ],
+  "plugins": [
+    "plugins/markdown"
+  ],
   "recurseDepth": 10,
   "source": {
     "includePattern": ".+\\.js$",
diff --git a/lib/browser.js b/lib/browser.js
index 5943716..1dba54e 100644
--- a/lib/browser.js
+++ b/lib/browser.js
@@ -21,6 +21,9 @@ export default class BrowserPageOpener {
   #window
   #coverageKey
 
+  /**
+   * @param {Window} window - the global (browser) window object
+   */
   constructor(window) {
     const covKey = getCoverageKey(window)
 
diff --git a/lib/jsdom.js b/lib/jsdom.js
index b503967..827e7e1 100644
--- a/lib/jsdom.js
+++ b/lib/jsdom.js
@@ -61,7 +61,7 @@ export default class JsdomPageOpener {
   /**
    * Creates a JsdomPageOpener from a dynamically imported jsdom module
    * @param {object} jsdom - dynamically imported jsdom module
-   * @param {jsdom.JSDOM} jsdom.JSDOM - the JSDOM class
+   * @param {object} jsdom.JSDOM - JSDOM class from the jsdom module
    */
   constructor({ JSDOM }) {
     this.#JSDOM = JSDOM
@@ -91,7 +91,7 @@ export default class JsdomPageOpener {
    * Dynamically imports ECMAScript modules.
    * @param {Window} window - the jsdom window object
    * @param {Document} document - the jsdom window.document object
-   * @returns {Promise} - resolves after importing all ECMAScript modules
+   * @returns {Promise<void>} - resolves after importing all ECMAScript modules
    * @throws if importing any ECMAScript modules fails
    */
   #importModules(window, document) {
@@ -125,8 +125,11 @@ export default class JsdomPageOpener {
         // register closures over window and document, or specific document
         // elements. That would ensure they remain defined even after we remove
         // window and document from globalThis.
+        //
+        // @ts-expect-error
         globalThis.window = window
         globalThis.document = document
+        const Event = globalThis.window.Event
 
         try { await importModules(document) }
         catch (err) { reject(err) }
@@ -137,7 +140,7 @@ export default class JsdomPageOpener {
         // DOMContentLoaded event listeners and have them fire here.
         //
         // We eventually fire the 'load' event again too for the same reason.
-        document.dispatchEvent(new window.Event(
+        document.dispatchEvent(new Event(
           'DOMContentLoaded', {bubbles: true, cancelable: false}
         ))
 
@@ -145,12 +148,14 @@ export default class JsdomPageOpener {
         // document variables. Because it's registered after any
         // DOMContentLoaded listeners have fired, it should execute after any
         // other 'load' listeners registered by any module code.
-        const resetGlobals = () => resolve(
-          delete globalThis.document, delete globalThis.window
-        )
+        const resetGlobals = () => {
+          delete globalThis.document
+          delete globalThis.window
+          resolve()
+        }
         window.addEventListener('load', resetGlobals, {once: true})
         window.dispatchEvent(
-          new window.Event('load', {bubbles: false, cancelable: false})
+          new Event('load', {bubbles: false, cancelable: false})
         )
       }
       window.addEventListener('load', importModulesOnEvent, {once: true})
@@ -163,10 +168,11 @@ export default class JsdomPageOpener {
  *
  * Only works with the `src` attribute; it will not execute inline code.
  * @param {Document} doc - the jsdom window.document object
- * @returns {Promise} - resolves after importing all ECMAScript modules in doc
- * @throws if importing any ECMAScript modules fails
+ * @returns {Promise<void[]>} - resolves after importing all modules in doc
+ * @throws if any module import fails
  */
 function importModules(doc) {
+  /** @type {HTMLScriptElement[]} */
   const modules = Array.from(doc.querySelectorAll('script[type="module"]'))
   return Promise.all(modules.filter(m => m.src).map(async m => {
     try { await import(m.src) }
diff --git a/package.json b/package.json
index b340bf7..8c13a52 100644
--- a/package.json
+++ b/package.json
@@ -1,15 +1,21 @@
 {
   "name": "test-page-opener",
-  "version": "1.0.3",
+  "version": "1.0.4",
   "description": "Enables an application's tests to open its own page URLs both in the browser and in Node.js using jsdom",
   "main": "index.js",
+  "types": "types/index.d.ts",
   "scripts": {
     "lint": "eslint --color --max-warnings 0 .",
     "test": "vitest",
     "test:ci": "eslint --color --max-warnings 0 . && vitest run -c ci/vitest.config.js && vitest run -c ci/vitest.config.browser.js",
-    "jsdoc": "jsdoc-cli-wrapper -c jsdoc.json ."
+    "jsdoc": "jsdoc-cli-wrapper -c jsdoc.json .",
+    "prepack": "npx -p typescript tsc ./index.js --allowJs --declaration --declarationMap --emitDeclarationOnly --outDir types"
   },
-  "files": [ "index.js", "lib/*" ],
+  "files": [
+    "index.js",
+    "lib/*",
+    "types/*"
+  ],
   "keywords": [
     "testing",
     "jsdom",
@@ -35,6 +41,7 @@
     "eslint-plugin-vitest": "^0.3.20",
     "jsdoc-cli-wrapper": "^1.0.4",
     "jsdom": "^23.1.0",
+    "typescript": "^5.3.3",
     "vite": "^5.0.11",
     "vitest": "^1.1.3",
     "webdriverio": "^8.27.0"
diff --git a/pnpm-lock.yaml b/pnpm-lock.yaml
index 67053a5..b61597c 100644
--- a/pnpm-lock.yaml
+++ b/pnpm-lock.yaml
@@ -40,6 +40,9 @@ devDependencies:
   jsdom:
     specifier: ^23.1.0
     version: 23.1.0
+  typescript:
+    specifier: ^5.3.3
+    version: 5.3.3
   vite:
     specifier: ^5.0.11
     version: 5.0.11
diff --git a/test/browser.test.js b/test/browser.test.js
index 68eed81..9ffc54b 100644
--- a/test/browser.test.js
+++ b/test/browser.test.js
@@ -4,7 +4,7 @@
  * file, You can obtain one at https://mozilla.org/MPL/2.0/.
  */
 
-import { DEFAULT_COVERAGE_KEY, getCoverageKey } from '../lib/browser'
+import { DEFAULT_COVERAGE_KEY, getCoverageKey } from '../lib/browser.js'
 import { describe, expect, test } from 'vitest'
 
 describe('getCoverageKey', () => {
diff --git a/test/event-ordering-demo/main.js b/test/event-ordering-demo/main.js
index 3c3bda6..de49011 100755
--- a/test/event-ordering-demo/main.js
+++ b/test/event-ordering-demo/main.js
@@ -1,4 +1,5 @@
 #!/usr/bin/env node
+/* eslint-env browser */
 /*
  * This Source Code Form is subject to the terms of the Mozilla Public
  * License, v. 2.0. If a copy of the MPL was not distributed with this
@@ -46,8 +47,9 @@ const { window } = await JSDOM.fromFile(
   pagePath, {resources: 'usable', runScripts: 'dangerously'}
 )
 const document = window.document
-const modulePath = document.querySelector('script[type="module"]').src
-const importPromise = import(modulePath)
+/** @type {HTMLScriptElement} */
+const moduleElem = document.querySelector('script[type="module"]')
+const importPromise = import(moduleElem.src)
 
 print(`document.readyState === ${document.readyState}`)
 document.addEventListener('DOMContentLoaded', () => print('DOMContentLoaded'))
diff --git a/test/jsdom.test.js b/test/jsdom.test.js
index fa8fa9a..4e311f9 100644
--- a/test/jsdom.test.js
+++ b/test/jsdom.test.js
@@ -4,7 +4,7 @@
  * file, You can obtain one at https://mozilla.org/MPL/2.0/.
  */
 
-import JsdomPageOpener from '../lib/jsdom'
+import JsdomPageOpener from '../lib/jsdom.js'
 import { beforeAll, describe, expect, test } from 'vitest'
 
 describe.skipIf(globalThis.window !== undefined)('JsdomPageOpener', () => {
diff --git a/test/main.test.js b/test/main.test.js
index 22b8f3b..702c421 100644
--- a/test/main.test.js
+++ b/test/main.test.js
@@ -10,7 +10,7 @@ import TestPageOpener from '../index.js'
 describe('TestPageOpener', () => {
   let opener
 
-  beforeAll(async () => opener = await TestPageOpener.create('/basedir/'))
+  beforeAll(async () => {opener = await TestPageOpener.create('/basedir/')})
   afterEach(() => opener.closeAll())
 
   test('loads page with module successfully', async () => {
@@ -18,7 +18,9 @@ describe('TestPageOpener', () => {
     const appElem = document.querySelector('#app')
     const linkElem = document.querySelector('#app p a')
 
+    expect(appElem).not.toBeNull()
     expect(appElem.textContent).toContain('Hello, World!')
+    expect(linkElem).not.toBeNull()
     expect(linkElem.href).toContain('%22Hello,_World!%22')
   })
 
diff --git a/vite.config.js b/vite.config.js
index 7ffe66f..4752e8b 100644
--- a/vite.config.js
+++ b/vite.config.js
@@ -1,3 +1,4 @@
+// @ts-nocheck
 import { defineConfig } from 'vite'
 import { configDefaults } from 'vitest/config'
 import fs from 'node:fs'