Thewindow property of aWindow 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 aglobal object. This means:

1. Global variables of your script are, in fact, properties ofwindow:

   js

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

2. You can access the built-in properties of the window object without having to prefix them withwindow.:

   js

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

The point of having thewindow 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 manuallet 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('https://google.com/'). You'd have to useopen('https://google.com/') 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", aJavaScript 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.

This page was last modified onMay 23, 2025 byMDN contributors.