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jQuery里面keypress与keydown区别

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.