onKeyDown

事件适用对象	document, Image, Link, Textarea
实现版本	Navigator 4.0

参数

handlerText

JavaScript 代码或对一个 JavaScript 函数的调用。

type	标明了事件的类型。
target	标明了事件原来发送的对象。
layerX, layerY, pageX, pageY, screenX, screenY	For an event over a window, these represent the cursor location at the time the event occurred. For an event over a form, they represent the position of the form element.
which	Represents the ASCII value of the key pressed. To get the actual letter, number, or symbol of the pressed key, use the String.fromCharCode 方法。 To set this 属性 when the ASCII value is unknown, use the String.charCodeAt 方法。
modifiers	Contains the list of modifier keys held down when the event occurred.