globalThis in JavaScript: Why It Exists

globalThis in JavaScript: Why It Exists

Before globalThis, accessing the global object required different code in different environments. globalThis (ES2020) fixes that.

The Problem

The global object has different names:

• Browsers: window (or self in workers).
• Node.js: global.
• Web Workers: self.

Code that needed the global object had to detect the environment:

const g = typeof window !== "undefined"
  ? window
  : typeof global !== "undefined"
    ? global
    : typeof self !== "undefined"
      ? self
      : undefined;

This was verbose and error-prone.

The Solution: globalThis

globalThis.setTimeout; // works in browsers, Node, workers
globalThis.myGlobal = 42;

globalThis always refers to the global object, regardless of environment. It is the standard way to access globals portably.

What Lives on globalThis

All the built-in globals: Object, Array, Math, JSON, Promise, console, setTimeout, fetch (in browsers). Plus any var-declared globals in non-module scripts.

In Modules

In ES modules, top-level this is undefined. If you need the global object, use globalThis:

// module.js
console.log(this);       // undefined
console.log(globalThis); // the global object

Should You Use It?

Mostly no. Polluting the global object is a bad practice. Use it when:

• Writing library code that needs a global reference.
• Polyfilling a missing global.
• Detecting environment capabilities.

The Takeaway

globalThis is the portable way to access the global object across browsers, Node.js, and workers. It replaces the old window/global/self detection pattern. Use it sparingly, since global pollution is a code smell.