Difference between revisions of "JavaScript Window Object"

Revision as of 18:36, 9 May 2007

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 achieve the same thing:

window.alert();
alert()

JavaScript window Object Properties

The JavaScript window object contains a number of properties that can be inspected and used in a script:

• window.closed - Used when handling multiple windows, this property indicates whether a window has been closed or not.

• window.defaultstatus / window.status - defaultstatus specifies the default message displayed in the browser status bar. status specifies a temporary message to display in the browser status bar in place of the default. Disabled in many browsers.

• window.frames[] - If the window contains frames this array holds the arrary of frame objects (see JavaScript Arrays details on accessing arrays).

• window.name - Windows opened by a script must be given a name. This property contains the name of the corresponding window object.

• window.opener - When a window has been opened in a script contained in another window, this property of the child window contains a reference window which opened it.

• window.parent - When working with frames in a window this property contains a reference to the window object that contains the frame.

• window.screen - An object which contains information about the screen on which the window is displays (properties contained in this object include height, width, availHeight, availWidth and colorDepth).

• window.self - A reference to the current window.

• window.top - A reference to the top-level window when working with frames.

Opening Browser Windows using JavaScript

A new browser window can be opened from a JavaScript script using the open() method of the window object. The syntax for opening a new window is as follows:

newWindowObj = window.open("URL", "WindowName", "feature, feature, feature ... ");

The following provides an explanation of the arguments passed through to the open() method:

• URL - Specifies the URL of the web page to be loaded into the new window. If no URL is specified a blank window is loaded.

• WindowName - Specifies the window name and is used to refer to the window.

• features - A comma separated list of features that allow you to customize the appearance of the window. Options are: