Web/API/Window/window

The window property of a Window object points to the window object itself. Thus, the following expressions all return the same window object:

window.window
window.window.window
window.window.window.window
// ...

In web pages, the window object is also a global object. This means:

1. global variables of your script are in fact properties of window:

   var global = {data: 0};
   alert(global === window.global); // displays "true"

2. you can access built-in properties of the window object without having to type window. prefix:

   setTimeout("alert('Hi!')", 50); // equivalent to using window.setTimeout.
   alert(window === window.window); // displays "true"

The point of having the window property refer to the object itself, was likely to make it easy to refer to the global object. Otherwise, you'd have to do a manual var window = this; assignment at the top of your script.

Another reason, is that without this property you wouldn't be able to write, for example, "window.open('http://google.com/')". You'd have to use "open('http://google.com/')%22 instead.

Yet another reason to use this property, is for libraries which wish to offer OOP-versions, and non-OOP versions (especially JavaScript modules). For example, if we refer to "this.window.location.href", a JavaScript module could define a property called "window" inside of a class it defined (since no global "window" variable exists for it by default) which could be created after passing in a window object to the module class' constructor.  Thus, "this.window" inside of its functions would refer to that window object. In the non-namespaced version, "this.window" would refer back to "window", and also be able to readily get the document location. Another advantage, is that the objects of such a class (even if the class were defined outside of a module) could change their reference to the window at will, they would not be able to do this if they had hard-coded a reference to "window". The default in the class could still be set as the current window object.

Specifications

Specification	Status	Comment
HTML Living StandardThe definition of 'Window.window' in that specification.	Living Standard	No difference from the latest snapshot HTML 5.1
HTML 5.1The definition of 'Window.window' in that specification.	Recommendation	No difference from the HTML5
HTML5The definition of 'Window.window' in that specification.	Recommendation	First snapshot containing the definition of Window.window.

Browser compatibility

The compatibility table on this page is generated from structured data. If you'd like to contribute to the data, please check out https://github.com/mdn/browser-compat-data and send us a pull request.

Update compatibility data on GitHub

	Desktop						Mobile
	Chrome	Edge	Firefox	Internet Explorer	Opera	Safari	Android webview	Chrome for Android	Firefox for Android	Opera for Android	Safari on iOS	Samsung Internet
window	Chrome Full support 1	Edge Full support 12	Firefox Full support 1	IE Full support 4	Opera Full support ≤12.1	Safari Full support 3	WebView Android Full support 1	Chrome Android Full support 18	Firefox Android Full support 4	Opera Android Full support ≤12.1	Safari iOS Full support 1	Samsung Internet Android Full support 1.0

Legend

Full support  

Full support

Window.window by Mozilla Contributors is licensed under CC-BY-SA 2.5.