The Browser Object Model (BOM) is a collection of objects that give you access to the browser and the computer screen. These objects are accessible through the global object window.
As you know already, in JavaScript there's a global object provided by the host environment. In the browser environment, this global object is accessible using window. All global variables are also accessible as properties of the window object as follows:
> window.somevar = 1; 1 > somevar; 1
Also, all of the core JavaScript functions (discussed in Chapter 2, Primitive Data Types, Arrays, Loops, and Conditions) are methods of the global object. Have a look at the following code snippet:
> parseInt('123a456');
123
> window.parseInt('123a456');
123
In addition to being a reference to the global object, the window object also serves a second purpose providing information about the browser environment. There's a window object for every frame, iframe...