The window object was introduced when JavaScript was made available at version 1.0. It has been revised several times and is likely to gain new functionality with every release.

This object is added to the scope chain as the global object when scripts are executed in a web browser. This means that the properties and methods are available without needing the window prefix.

In a web browser this IS the global object. Adding properties (variables) during script execution adds them to the window object for the window in which the page containing the script is loaded.

The window represents the browser container that the document object lives in.

Since the on-screen window persists as long as the window is open, you might think it may be a useful place to store some session state data between documents. Clearly, storing session data in a document object is no use if the document is going to be discarded and replaced. However, anything created by a script belonging to a window is going to get zapped when the document goes away, so you cannot store persistent values in the window object like that because the global object for a web page is recreated each time a page is loaded.

Storing session state data is best accomplished with a frame-set and some accessor scripts that are called within it.

Event handling support via properties containing function objects was added to window objects in version 1.1 of JavaScript.

Warnings:

• Be aware that if you store a reference to a window object and the window is closed, if you don't dispose of the reference to the window object then it cannot be garbage collected. A window object with no associated window is not much use unless you need to keep the object persistent due to having added some properties to it. If this is the case, then, arguably, the window object was the wrong place to put such things.