JavaScript: The Definitive Guide, 6th Edition

Client-Side JavaScript

The Window object is the main entry point to all client-side JavaScript features and APIs. It represents a web browser window or frame, and you can refer to it with the identifier window. The Window object defines properties like location, which refers to a Location object that specifies the URL currently displayed in the window and allows a script to load a new URL into the window:

// Set the location property to navigate to a new web page
window.location = "http://www.oreilly.com/";

The Window object also defines methods like alert(), which displays a message in a dialog box, and setTimeout(), which registers a function to be invoked after a specified amount of time:

// Wait 2 seconds and then say hello
setTimeout(function() { alert("hello world"); }, 2000);

Notice that the code above does not explicitly use the window property. In client-side JavaScript, the Window object is also the global object. This means that the Window object is at the top of the scope chain and that its properties and methods are effectively global variables and global functions. The Window object has a property named window that always refers to itself. You can use this property if you need to refer to the window object itself, but it is not usually necessary to use window if you just want to refer to access properties of the global window object.

There are a number of other important properties, methods, and constructors defined by the Window object. See Chapter 14 for complete details. ...