jQuery里面keypress与keydown区别

看了jQuery的源代码,其实jQuery里面的keypress和keydown是直接来自于原生js里面相应的onkeypress和onkeydown,没有特殊修改。所以下文讲的就是原生js里面的这两个事件的区别。

具体区别

  1.  一个放开一个没有放开,onkeydown 先于 onkeypress 发生。但是如果一直按住某个键不放,两个事件都是会不断触发的。
  2. onkeypress 事件在用户按下并放开任何字母数字键时发生。但是系统按钮(例如:箭头键、功能键)无法得到识别。
  3. onkeydown 事件在用户按下任何键盘键(包括系统按钮)时发生,捕获的 keyCode 不区分字母大小,而 onkeypress 区分。

补充一下,有时候我们为了验证表单数据,就需要根据按键动作来检测输入的数据,如果用keypress和keydown,验证这个动作发生在这个键输入结束之前,就是导致相应的检测函数只能检测到按下这个键之前的数据,所以这时候应该用keyup动作,不过这也从侧面看出keypress和keydown在动作上是差不多的,只是能够获取的键值不同。个人感觉,keydown检测的是键盘的实体键(实体键大小写a和A是一个键嘛),也验证了前面的话。

可以自己测试一下:

<!doctype html>
<html lang="en">
<head>
<meta charset="UTF-8">
<title>按键测试</title>
<script src="jquery.js"></script>
</head>
<body>
<div>次数</div>
<script>
i=0;
$(window).keypress( function () { $('div').html(i++) } );
</script>
</body>
</html>

下面是微软的定义的keypress和keydown的按键区别。
onkeypress
As of Microsoft® Internet Explorer 4.0, the onkeypress event fires and can be canceled for the following keys:

Letters: A - Z (uppercase and lowercase)
Numerals: 0 - 9
Symbols: ! @ # $ % ^ & * ( ) _ - + = < [ ] { } , . / ? \ | ' ` " ~
System: ESC, SPACEBAR, ENTER

onkeydown
As of Microsoft® Internet Explorer 4.0, the onkeydown event fires for the following keys:

Editing: DELETE, INSERT
Function: F1 - F12
Letters: A - Z (uppercase and lowercase)
Navigation: HOME, END, LEFT ARROW, RIGHT ARROW, UP ARROW, DOWN ARROW
Numerals: 0 - 9
Symbols: ! @ # $ % ^ & * ( ) _ - + = < [ ] { } , . / ? \ | ' ` " ~
System: ESC, SPACEBAR, SHIFT, TAB

As of Internet Explorer 5, the event also fires for the following keys:

Editing: BACKSPACE
Navigation: PAGE UP, PAGE DOWN
System: SHIFT+TAB

As of Internet Explorer 5, this event can be canceled for the following keys and key combinations by specifying event.returnValue=false:

Editing: BACKSPACE, DELETE
Letters: A - Z (uppercase and lowercase)
Navigation: PAGE UP, PAGE DOWN, END, HOME, LEFT ARROW, RIGHT ARROW, UP ARROW, DOWN ARROW
Numerals: 0 - 9
Symbols: ! @ # $ % ^ & * ( ) _ - + = < [ ] { } , . / ? \ | ' ` " ~
System: SPACEBAR, ESC, TAB, SHIFT+TAB

You can cancel all keys that fire the onkeydown event in HTML Applications, including most accelerator keys, such as ALT+F4.

In Internet Explorer 4.0, you cannot cancel the onkeydown event, but you can use the onkeypress event to cancel keyboard events.

 

标签: jquery, 事件, keypress, keydown

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