JS globalThis
In this page:
globalThis.propertyName = value;
globalThis.propertyName;What Is globalThis
globalThis is a standard property that refers to the global object no matter which JavaScript environment the code runs in, unifying what used to require different names per platform.
Example: What Is globalThis
console.log(typeof globalThis); // "object" in every environmentglobalThis in Node.js
In Node.js, globalThis points to the same global object you'd otherwise access as global, giving Node code a way to reference global state without a Node-specific identifier that wouldn't work in a browser.
Example: globalThis in Node.js
// In Node.js: globalThis === global
console.log(typeof globalThis);globalThis and Browser Code
In browsers, globalThis refers to the same object as window (or self inside a worker), so browser code can use it without assuming a specific browser global exists.
Example: globalThis and Browser Code
// In browsers: globalThis === window
console.log(globalThis === window);Portable Global Access
Because globalThis works identically everywhere, code that needs to check for or attach to the global object — like a polyfill — can do so without environment-detection branching.
Example: Portable Global Access
// Check whether `!globalThis.myPolyfill`
// Check whether `!globalThis.myPolyfill`
if (!globalThis.myPolyfill) {
// Assign `function () { return "polyfilled"; }` to `globalThis.myPolyfill`
// Assign `function () { return "polyfilled"; }` to `globalThis.myPolyfill`
globalThis.myPolyfill = function () { return "polyfilled"; };
}
// Print `globalThis.myPolyfill()` to the console
// Print `globalThis.myPolyfill()` to the console
console.log(globalThis.myPolyfill());Best Practices with globalThis
Prefer explicit imports and modules over touching globalThis directly; reserve it for genuine cross-environment library code that must interact with the global object safely.
Example: Best Practices with globalThis
// Prefer modules/imports over touching globalThis directly
import { helper } from './utils.js';
console.log(helper());- Using
windowin code that also runs in Node.js, which throwsReferenceError; useglobalThis. - Creating accidental global properties on
globalThis, which can clash with other scripts. - Expecting
letandconstat the top level to appear onglobalThis, when onlyvarand function declarations may.
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