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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>

亲自试一试

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>

亲自试一试

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

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