Global object

A global object is an object that always exists in the global scope.

In JavaScript, there's always a global object defined. In a web browser, when scripts create global variables defined with the var keyword, they're created as members of the global object. (In Node.js this is not the case.) The global object's interface depends on the execution context in which the script is running. For example:

  • In a web browser, any code which the script doesn't specifically start up as a background task has a Window as its global object. This is the vast majority of JavaScript code on the Web.
  • Code running in a Worker has a WorkerGlobalScope object as its global object.
  • Scripts running under Node.js have an object called global as their global object.

The globalThis global property allows one to access the global object regardless of the current environment.

var statements and function declarations at the top level create properties of the global object. On the other hand, let and const declarations never create properties of the global object.

The properties of the global object are automatically added to the global scope.

In JavaScript, the global object always holds a reference to itself:

console.log(globalThis === globalThis.globalThis); // true (everywhere)
console.log(window === window.window); // true (in a browser)
console.log(self === self.self); // true (in a browser or a Web Worker)
console.log(frames === frames.frames); // true (in a browser)
console.log(global ===; // true (in Node.js)

See also