globalThis

Published · tagged with ECMAScript ES2020

If you’ve written JavaScript for use in a web browser before, you may have used window to access the global this. In Node.js, you may have used global. If you’ve written code that must work in either environment, you may have detected which of these is available, and then used that — but the list of identifiers to check grows with the number of environments and use cases you want to support. It gets out of hand quickly:

// A naive attempt at getting the global `this`. Don’t use this!
const getGlobalThis = () => {
if (typeof globalThis !== 'undefined') return globalThis;
if (typeof self !== 'undefined') return self;
if (typeof window !== 'undefined') return window;
if (typeof global !== 'undefined') return global;
// Note: this might still return the wrong result!
if (typeof this !== 'undefined') return this;
throw new Error('Unable to locate global `this`');
};
const theGlobalThis = getGlobalThis();

For more details on why the above approach is insufficient (as well as an even more complicated technique), read a horrifying globalThis polyfill in universal JavaScript.

The globalThis proposal introduces a unified mechanism to access the global this in any JavaScript environment (browser, Node.js, or something else?), regardless of the script goal (classic script or module?).

const theGlobalThis = globalThis;

Note that modern code might not need access to the global this at all. With JavaScript modules, you can declaratively import and export functionality instead of messing with global state. globalThis is still useful for polyfills and other libraries that need global access.

globalThis support