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JavaScript 事件
Posted by 撒得一地 on 2016年5月29日 in JavaScript教程
事件是什么？
HTML 与 JavaScript 的的相互作用，是通过用户或浏览器操作页面时出现的事件来进行处理的。
页面加载时，它被称为一个事件。当用户点击一个按钮时，点击也是一个事件。其他例子包括像按任何键，关闭窗口，调整窗口等也是事件。
开发人员可以使用这些事件来执行 JavaScript 编码响应，将点击按钮、关闭窗口、数据验证和几乎任何其他可以想象的响应类型等消息显示给用户。
事件是文档对象模型 (DOM) 级别3 的一部分，每个 HTML 元素包含一组可以触发 JavaScript 代码的事件。
为了更好地理解 HTML 事件，在这里我们将会看到几个示例，以了解事件和 JavaScript 的关系：
onclick 事件类型
这是最常用的事件类型，当用户单击鼠标左边的按钮时触发。你可以对此事件发生时进行验证、警告等。
示例
请尝试下面的示例。
<html>
<head>
<script type="text/javascript">
<!--
function sayHello() {
alert("Hello World")
}
//-->
</script>
</head>
<body>
<p>Click the following button and see result</p>
<form>
<input type="button" onclick="sayHello()" value="Say Hello" />
</form>
</body>
</html>
onsubmit 事件类型
onsubmit 是当你尝试提交表单时出现的事件。你可以通过这种事件类型对你提交的表单进行验证。
示例
下面的示例演示如何使用 onsubmit。在将数据提交到 web 服务器之前，我们先调用 validate() 验证函数。如果 validate() 函数返回 true，则提交表单，否则它不会提交表单的数据。
<html>
<head>
<script type="text/javascript">
<!--
function validation() {
all validation goes here
.........
return either true or false
}
//-->
</script>
</head>
<body>
<form method="POST" action="t.cgi" onsubmit="return validate()">
.......
<input type="submit" value="Submit" />
</form>
</body>
</html>
onmouseover 和 onmouseout
这两个事件类型将帮助您创建很好的效果，该效果基于图像或文本等。onmouseover 是当你把你的鼠移到任何元素时进行事件触发，onmouseout 是当你将鼠标从某个元素移开时进行事件触发。请尝试下面的示例。
<html>
<head>
<script type="text/javascript">
<!--
function over() {
document.write ("Mouse Over");
}
function out() {
document.write ("Mouse Out");
}
//-->
</script>
</head>
<body>
<p>Bring your mouse inside the division to see the result:</p>
<div onmouseover="over()" onmouseout="out()">
<h2> This is inside the division </h2>
</div>
</body>
</html>
HTML 5 标准事件
这里列出了标准的 HTML5 事件供您参考。在这里 script 表明了执行具体某个 Javascript 函数来响应该事件。
| Attribute | Value | Description |
|---|---|---|
| Offline | script | Triggers when the document goes offline |
| Onabort | script | Triggers on an abort event |
| onafterprint | script | Triggers after the document is printed |
| onbeforeonload | script | Triggers before the document loads |
| onbeforeprint | script | Triggers before the document is printed |
| onblur | script | Triggers when the window loses focus |
| oncanplay | script | Triggers when media can start play, but might has to stop for buffering |
| oncanplaythrough | script | Triggers when media can be played to the end, without stopping for buffering |
| onchange | script | Triggers when an element changes |
| onclick | script | Triggers on a mouse click |
| oncontextmenu | script | Triggers when a context menu is triggered |
| ondblclick | script | Triggers on a mouse double-click |
| ondrag | script | Triggers when an element is dragged |
| ondragend | script | Triggers at the end of a drag operation |
| ondragenter | script | Triggers when an element has been dragged to a valid drop target |
| ondragleave | script | Triggers when an element is being dragged over a valid drop target |
| ondragover | script | Triggers at the start of a drag operation |
| ondragstart | script | Triggers at the start of a drag operation |
| ondrop | script | Triggers when dragged element is being dropped |
| ondurationchange | script | Triggers when the length of the media is changed |
| onemptied | script | Triggers when a media resource element suddenly becomes empty. |
| onended | script | Triggers when media has reach the end |
| onerror | script | Triggers when an error occur |
| onfocus | script | Triggers when the window gets focus |
| onformchange | script | Triggers when a form changes |
| onforminput | script | Triggers when a form gets user input |
| onhaschange | script | Triggers when the document has change |
| oninput | script | Triggers when an element gets user input |
| oninvalid | script | Triggers when an element is invalid |
| onkeydown | script | Triggers when a key is pressed |
| onkeypress | script | Triggers when a key is pressed and released |
| onkeyup | script | Triggers when a key is released |
| onload | script | Triggers when the document loads |
| onloadeddata | script | Triggers when media data is loaded |
| onloadedmetadata | script | Triggers when the duration and other media data of a media element is loaded |
| onloadstart | script | Triggers when the browser starts to load the media data |
| onmessage | script | Triggers when the message is triggered |
| onmousedown | script | Triggers when a mouse button is pressed |
| onmousemove | script | Triggers when the mouse pointer moves |
| onmouseout | script | Triggers when the mouse pointer moves out of an element |
| onmouseover | script | Triggers when the mouse pointer moves over an element |
| onmouseup | script | Triggers when a mouse button is released |
| onmousewheel | script | Triggers when the mouse wheel is being rotated |
| onoffline | script | Triggers when the document goes offline |
| onoine | script | Triggers when the document comes online |
| ononline | script | Triggers when the document comes online |
| onpagehide | script | Triggers when the window is hidden |
| onpageshow | script | Triggers when the window becomes visible |
| onpause | script | Triggers when media data is paused |
| onplay | script | Triggers when media data is going to start playing |
| onplaying | script | Triggers when media data has start playing |
| onpopstate | script | Triggers when the window's history changes |
| onprogress | script | Triggers when the browser is fetching the media data |
| onratechange | script | Triggers when the media data's playing rate has changed |
| onreadystatechange | script | Triggers when the ready-state changes |
| onredo | script | Triggers when the document performs a redo |
| onresize | script | Triggers when the window is resized |
| onscroll | script | Triggers when an element's scrollbar is being scrolled |
| onseeked | script | Triggers when a media element's seeking attribute is no longer true, and the seeking has ended |
| onseeking | script | Triggers when a media element's seeking attribute is true, and the seeking has begun |
| onselect | script | Triggers when an element is selected |
| onstalled | script | Triggers when there is an error in fetching media data |
| onstorage | script | Triggers when a document loads |
| onsubmit | script | Triggers when a form is submitted |
| onsuspend | script | Triggers when the browser has been fetching media data, but stopped before the entire media file was fetched |
| ontimeupdate | script | Triggers when media changes its playing position |
| onundo | script | Triggers when a document performs an undo |
| onunload | script | Triggers when the user leaves the document |
| onvolumechange | script | Triggers when media changes the volume, also when volume is set to "mute" |
| onwaiting | script | Triggers when media has stopped playing, but is expected to resume |