JavaScript Window Object

The JavaScript window object sits at the top of the JavaScript Object hierarchy and represents the browser window (or windows if you have more than one browser window open at any one time). Up until this chapter we have focused on the internals and syntax of JavaScript. In this chapter we will begin to make things happen on the screen (which, after all, is one of the main purposes of JavaScript). The window object allows developers to perform tasks such as opening and closing browser windows, displaying alert and prompt dialogs and set up timeouts (specifying an action to take place after a specified period of time).

Referencing the JavaScript window Object

As covered in JavaScript Object Basics it is usually necessary to use dot-notation when accessing properties or methods of an object. For example the following script fragment accesses the write() method of the document object:

document.write("Hello");

The window object is the top-level object of the object hierarchy. As such, whenever an object method or property is referenced in a script without the object name and dot prefix it is assumed by JavaScript to be a member of the window object. This means, for example, that when calling the window alert() method to display an alert dialog the window. prefix is not mandatory. Therefore the following method calls achive the same thing:

window.alert();
alert()