References

Beginner-friendly references for web development, with live, editable examples.

The JavaScript globalThis object

Object JavaScript All modern browsers Updated
Quick answer

The globalThis keyword is a standard, universal reference to the global object that works everywhere — it's window in browsers, global in Node, and self in web workers. Use globalThis instead of those environment-specific names when you need to access or define a global in portable code.

Overview

globalThis solves an old portability headache: the global object had a different name in every environment. In a browser it was window (or self in workers); in Node it was global. Code that needed the global object had to sniff the environment or use brittle tricks. globalThis is the single, standard name that points to the global object everywhere.

You reach for it when you genuinely need the global scope in code that must run across environments — a library checking for a global feature, a polyfill installing itself, or detecting whether you're in a browser (typeof globalThis.document !== "undefined"). In ordinary app code that targets one environment, you can still just use window; globalThis matters most for portable libraries and shared modules.

A word of caution that applies to all global access: relying on globals is usually a smell. Modules, imports and explicit parameters are cleaner than reaching into global scope. Use globalThis when you truly need the global object, not as a convenient dumping ground for shared state.

Syntax

globalThis        // the global object, everywhere

globalThis.window  // browser
globalThis.global  // Node (older code)
globalThis.self    // web workers

// feature detection
if (typeof globalThis.fetch === "function") { /* ... */ }

Example

Live example 
<pre id="out" style="font:14px ui-monospace,monospace"></pre>
<script>
  const inBrowser = typeof globalThis.document !== 'undefined';
  const hasFetch = typeof globalThis.fetch === 'function';

  document.getElementById('out').textContent =
    'globalThis === window? ' + (globalThis === window) + '\n' +
    'in a browser? ' + inBrowser + '\n' +
    'has fetch?    ' + hasFetch;
</script>

Best practices

  • Use globalThis for portable code that must run in browsers, Node and workers.
  • Prefer it over environment-specific names (window, global, self) in shared libraries.
  • Use it for feature detection: typeof globalThis.someAPI.
  • Avoid globals in general — modules and explicit parameters are cleaner than global state.

Frequently asked questions

What is globalThis in JavaScript?
A standard reference to the global object that works in every environment — window in browsers, global in Node, self in workers.
When should I use globalThis?
In code that must run across environments, for accessing the global object or feature detection. In single-environment app code, window is fine.
Is globalThis the same as window?
In a browser, yes — globalThis is window. In Node it's global, and in a worker it's self. That portability is the point.
Should I store data on globalThis?
Generally no. Relying on global state is a code smell — prefer modules, imports and explicit parameters.
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