Availability

JavaScript 1.2; HTML 4.0

Synopsis

<element onkeydown="handler" ... > 
element.onkeydown

Description

The onkeydown property of an HTMLElement object specifies an event handler function that is invoked when the user presses a key over the element.

The initial value of this property is a function that contains the JavaScript statements specified by the onkeydown attribute of the HTML tag that defined the object. When an event handler function is defined by an HTML attribute, it is executed in the scope of element rather than in the scope of the containing window.

In the Netscape 4 event model, the onkeydown handler function is passed an Event object as an argument. In the IE event model, no argument is passed, but the applicable Event object is available as the event property of the Window object that contains the element.

The character code of the key pressed is contained in the which property of the Event object in Netscape and in the keyCode property of the Event object in IE. You can convert this keycode to a string with String.fromCharCode( ). The modifier keys in effect can be determined from the Event.modifiers property in Netscape or with Event.shiftKey( ) and related methods in IE.

In the Netscape event model, you can cancel processing of the keystroke by returning false from this handler. In the IE event model, you cancel processing by setting Event.returnValue to false. In IE, this handler may return an alternate keycode that is used in place of the key actually pressed by the user.

You can often use the onkeypress event handler instead of the onkeydown and onkeyup handlers.

See Also

Event, HTMLElement.onkeypress; Chapter 19