Javascript 的addEventListener()及attachEvent()
大家都知道事件的用法就是当某个事件(状况)被触发了之后就会去执行某个Function, 尤其是Javascript, 在当红AJAX的催化下, 了解Javascript的Event用法更加重要, 在这里就大概介绍一下Javascript的Event用法.
从W3C的发展时间轴来看, DOM(Document Object Model)的模型可以分为两种, DOM 0 及 DOM 2. 从数字来看就可以知道DOM 0 当然是比较旧的协议, 我们可以从以下的表格来看:
DOM1 协定:
|
|
|
| Event Name |
Description |
| onblur() |
The element has lost focus (that is, it is not selected by the user). |
| onchange0 |
The element has either changed (such as by typing into a text field) or the element has lost focus. |
| onclick0 |
The mouse has been clicked on an element. |
| ondblclick() |
The mouse has been double-clicked on an element. |
| onfocus() |
The element has gotten focus. |
| onkeydown() |
A keyboard key has been pressed down (as opposed to released) while the element has focus. |
| onkeypress() |
A keyboard key has been pressed while the element has focus. |
| onkeyup() |
A keyboard key has been released while the element has focus. |
| onload() |
The element has loaded (document, frameset, or image). |
| onmousedown() |
A mouse button has been pressed. |
| onmousemove() |
The mouse has been moved. |
| onmouseout() |
The mouse has been moved off of or away from an element. |
| onmouseover() |
The mouse has moved over an element. |
| onmouseup() |
A mouse button has been released. |
| onreset() |
The form element has been reset, such as when a form reset button is pressed. |
| onresize() |
The window’s size has been changed. |
| onselect() |
The text of a form element has been selected. |
| onsubmit() |
The form has been submitted. |
| onunload() |
The document or frameset has been unloaded. |
DOM2 的进化:
| DOM 0 Event |
DOM 2 Event |
| onblur() |
blur |
| onfocus() |
focus |
| onchange() |
change |
| onmouseover() |
mouseover |
| onmouseout() |
mouseout |
| onmousemove() |
mousemove |
| onmousedown() |
mousedown |
| onmouseup() |
mouseup |
| onclick() |
click |
| ondblclick() |
dblclick |
| onkeydown() |
keydown |
| onkeyup() |
keyup |
| onkeypress() |
keypress |
| onsubmit() |
submit |
| onload() |
load |
| onunload() |
unload |
新的DOM2 用法可以addEventListener()这个函数来观察到:
addEventListener(event,function,capture/bubble);
参数event如上表所示, function是要执行的函数, capture与bubble分别是W3C制定得两种时间模式,简单来说capture就是从document的开始读到最后一行, 再执行事件, 而bubble则是先寻找指定的位置再执行事件.
capture/bubble的参数是布尔值, True表示用capture, False则是bubble.Windows Internet Explorer也有制定一种EventHandler, 是 attachEvent(), 格式如下:
window.attachEvent(”submit”,myFunction());
比较特别的是attachEvent不需要指定capture/bubble的参数, 因为在windows IE环境下都是使用Bubble的模式.这里用图像的Rollover例子来表现事件的用法:
<!DOCTYPE HTML PUBLIC “-//W3C//DTD HTML 4.01//EN”
“http://www.w3.org/TR/html4/strict.dtd“>
<html>
<head>
<title>Rollover</title>
<script type=”text/javascript”>function moveOver(imgObj) {
if (typeof window.addEventListener != “undefined”) {
imgObj.addEventListener(”mouseover”,function(){imgObj.src = imgObj.id +
“_over.png”;}, false);
imgObj.addEventListener(”mouseout”, function(){imgObj.src = imgObj.id +
“_default.png”;}, false);
} else {
imgObj.attachEvent(”onmouseover”,function(){imgObj.src = imgObj.id +
“_over.png”;});
imgObj.attachEvent(”onmouseout”, function(){imgObj.src = imgObj.id +
“_default.png”;});
}
}
function rollover() {
var images = document.getElementsByTagName(”img”);
var roll = new RegExp (”rollover”);
var preload = [];
for (var i = 0; i < images.length; i++) {
if (images[i].id.match(roll)) {
preload[i] = new Image();
preload[i].src = images[i].id + “_over.png”;
moveOver(images[i]);
}
}
}
if (typeof window.addEventListener != “undefined”) {
window.addEventListener(”load”,rollover,false);
} else {
window.attachEvent(”onload”,rollover)
}
</script>
</head>
<body>
<p><img id=”rollover_home” name=”img_home” src=”rollover_home_default.png”
alt=”Home”></p>
<p><img id=”rollover_about” name=”img_about” src=”rollover_about_default.png”
alt=”About”></p>
<p><img id=”rollover_blog” name=”img_blog” src=”rollover_blog_default.png”
alt=”Blog”></p>
<p><img id=”logo” name=”img_logo” src=”logo.png” alt=”Braingia Logo”></p>
</body>
</html>
上述的 typeof window.addEventListener != “undefined” 程序代码可以判断使用者的浏览器是否支持AddEventListener这个事件模型, 如果不支持就使用attachEvent.
W3C 及 IE 同时支持移除指定的事件, 用途是移除设定的事件, 格式分别如下:
W3C格式:
removeEventListener(event,function,capture/bubble);
Windows IE的格式如下:
detachEvent(event,function);
数据参考: Chapter 14 - Browsers and JavaScript, JavaScript Step by Step, by Steve Suehring