Should I check typeof document before using it?

For shared utility code, typeof document !== 'undefined' is a safe guard. In components, it can make the server and browser render different HTML, so prefer running DOM code after mount.

jsdom is more complete; happy-dom is faster but lacks some APIs. Start with jsdom and switch only if test speed matters and your tests pass.

Can you fix it for me?

If one bug is the whole problem, the App Fix Ticket covers it: a written diagnosis first, then the fix. If the app has more going on, the Launch Check is a written check of the whole app. Each issue found is rated critical, high, medium or low, with where it is and how it was confirmed. No issues worth fixing, no charge. If the Launch Check finds nothing rated medium or higher, Simon refunds the full $450. You keep the report either way. This applies to the first 10 Launch Checks bought after October 30, 2026.

“ReferenceError: document Is Not Defined”: Fix

Short answer

In Jest, set testEnvironment to jsdom (and install jest-environment-jsdom, which Jest 28 and later no longer bundle); in Vitest, set environment to jsdom or happy-dom. In a Node.js script that needs to read HTML, use a parser such as jsdom or cheerio instead of document. In Next.js, Nuxt or SvelteKit, move the DOM code into useEffect, onMounted or onMount so it only runs in the browser.

Where the code runs, and the fix

01
Jest tests running in the Node.js environment
“The default environment in Jest is a Node.js environment. If you are building a web app, you can use a browser-like environment through jsdom instead.” Jest, Configuration: testEnvironment
Tests for components that touch the DOM need a simulated browser. Set it for the whole project, or per file with a docblock at the top.
```
npm install -D jest-environment-jsdom

// jest.config.js
module.exports = { testEnvironment: 'jsdom' };

/**
 * @jest-environment jsdom
 */
```

Vitest tests in the default environment

Vitest also defaults to Node.js. Install jsdom or happy-dom and set the environment in the config, or per file with a comment.

// vitest.config.ts
import { defineConfig } from 'vitest/config';
export default defineConfig({ test: { environment: 'jsdom' } });

// or at the top of one test file
// @vitest-environment jsdom

A Node.js script that parses HTML

Node.js has no page and no document. To read or change HTML in a script, load it into a parser.

import { JSDOM } from 'jsdom';
const { document } = new JSDOM(html).window;
const title = document.querySelector('h1')?.textContent;

04
Server rendering in Next.js, Nuxt or SvelteKit
Components render on the server before the browser. Read document inside useEffect (React), onMounted (Vue) or onMount (Svelte), or load browser-only components on the client only.
```
useEffect(() => {
  document.title = `${count} new messages`;
}, [count]);
```

Checked against the vendor’s docs on November 8, 2026: Jest: Configuration (testEnvironment).

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JavaScript errorJavaScript: “ReferenceError: document is not defined”

Where the code runs, and the fix

Jest tests running in the Node.js environment

Vitest tests in the default environment

A Node.js script that parses HTML

Server rendering in Next.js, Nuxt or SvelteKit

Rather hand it over?

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