大家都知道事件的用法就是當某個事件(狀況)被觸發了之後就會去執行某個Function, 尤其是Javascript, 在當紅AJAX的催化下, 了解Javascript的Event用法更加重要, 在這裡就大概介紹一下Javascript的Event用法.

從W3C的發展時間軸來看, DOM(Document Object Model)的模型可以分為兩種, DOM 0 及 DOM 2. 從數字來看就可以知道DOM 0 當然是比較舊的協定, 我們可以從以下的表格來看:

DOM1 協定:

 

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 的進化:

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()這個函數來觀察到:

addEventListener(event,function,capture/bubble);

參數event如上表所示, function是要執行的函數, capture與bubble分別是W3C制定得兩種時間模式,簡單來說capture就是從document的開始讀到最後一行, 再執行事件, 而bubble則是先尋找指定的位置再執行事件.
capture/bubble的參數是布林值, True表示用capture, False則是bubble.Windows Internet Explorer也有制定一種EventHandler, 是 attachEvent(), 格式如下:

window.attachEvent("submit",myFunction());

比較特別的是attachEvent不需要指定capture/bubble的參數, 因為在windows IE環境下都是使用Bubble的模式.這裡用圖像的Rollover例子來表現事件的用法:

<!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" 程式碼可以判斷使用者的瀏覽器是否支援AddEventListener這個事件模型, 如果不支援就使用attachEvent.

W3C 及 IE 同時支援移除指定的事件, 用途是移除設定的事件, 格式分別如下:

W3C格式:

removeEventListener(event,function,capture/bubble);

Windows IE的格式如下:

detachEvent(event,function);

資料參考: Chapter 14 – Browsers and JavaScript, JavaScript Step by Step, by Steve Suehring

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