domdomdom

domdomdom

Evaluate JavaScript against an HTML page from the command line. Pipe in code, get back the truth, cue dramatic chipmunk!

echo "return document.querySelectorAll('h1').length" | domdomdom https://example.com

Powered by happy-dom. No browser binary, no Playwright install, no MCP server. Two TypeScript files, ~12KB on npm.

Why this exists

happy-dom almost works on Bun out of the box. Then you hit four walls. domdomdom fixes them so you don't have to:

1. Built-ins are missing. happy-dom's BrowserWindow on Bun starts with Object, Math, JSON, parseInt, SyntaxError etc. set to undefined. Its VMGlobalPropertyScript tries to copy them from globalThis, but inside Script.runInContext globalThis refers to the (empty) inner scope. Every querySelector throws TypeError because SyntaxError isn't on window. domdomdom enumerates Object.getOwnPropertyNames(globalThis) from the host realm and assigns each to the page window.
2. file:// doesn't fetch. page.goto('file:///abs/path.html') rejects. domdomdom reads HTML manually and uses page.content = plus page.url = to set up the page.
3. IIFE bundles silently break. happy-dom's HTML parser wraps every <script> body in function anonymous($happy_dom) { ... }. Top-level var foo = (() => { ... })() becomes a function-local — never reaches window. domdomdom extracts <script src> tags before page.content and runs them via page.evaluate() (uses Script.runInContext directly, preserves real script-top-level scope).
4. ES modules can't import. <script type="module" src="./foo.js"> can't be fetched from disk. domdomdom maps a synthetic http:// origin to the page directory via happy-dom's virtualServers so relative imports work.

Each of these is a one-line fix once you've found it. Finding them took an afternoon.

When to use this vs. alternatives

You want	Use this
Run a snippet against a real page, fast	domdomdom
Test code that uses document, window	domdomdom
Verify an IIFE bundle attaches to window	domdomdom
Layout, computed styles, screenshots	Playwright
Run untrusted JS safely	Playwright (sandbox) or a worker pool
Parse HTML without executing scripts	linkedom (faster)
Module bundling / build tooling	bun build / esbuild

Install

# global install
bun add -g domdomdom
npm install -g domdomdom

# one-off, no install
bunx domdomdom ./page.html
npx domdomdom https://example.com

# clone for development
git clone https://github.com/scruffymongrel/domdomdom && cd domdomdom && bun link

Runtime requirements

• Bun ≥ 1.3 — works out of the box.
• Node ≥ 23.6 (LTS: 24+) — uses Node's built-in TypeScript stripping. The shebang silences the experimental-feature warning automatically. Node 22 LTS users need node --experimental-strip-types set in NODE_OPTIONS, or just install via Bun.

No build step. The published package ships .ts source directly; both runtimes execute it natively.

CLI

domdomdom [options] [URL_OR_PATH]

Source	Interpretation
http(s)://...	fetched via happy-dom
./path.html	read from disk; relative scripts/modules resolved
--html '<...>'	inline HTML
(none)	about:blank

Code source	Interpretation
stdin	default; auto-return if a single expression
--script <f>	read user code from a file (no auto-return)

Flags

Flag	Effect
--inject <f>	preload a JS file in the window before user code; repeatable
--module	evaluate user code as ES module (allows top-level import)
--user-agent	override navigator.userAgent
--viewport WxH	override page viewport (e.g. 1024x768)
--timeout <ms>	time limit; 0 disables; default 5000
--no-console	drop console.* output instead of capturing it
--json	emit one JSON line: { ok, result?, error?, logs }
-h, --help	show help

Output contract