<script language="javascript">
function keyevent(){
if(event.keyCode==13)
alert("你按了回车键");
}
document.onkeydown = keyevent;//注册document.onkeydown事件
</script>
当用户按回车键时，就会执行keyevent()这个函数。可以做回车提交表单，或其它的事件！
keyCode是返回keydown何keyup事件发生的时候按键的代码，以及keypress 事件的Unicode字符；如果要使用组合键，则可以利用event.ctrlKey，event.shiftKey，event .altKey判断是否按下了ctrl键、shift键以及alt键.
| 常用keycode | |||
|---|---|---|---|
| key | code | key | code |
| left | 37 | up | 38 |
| right | 39 | down | 40 |
| 1 | 49 | 2 | 50 |
| 3 | 51 | a | 65 |
| shift | 16 | ctrl | 17 |
| alt | 18 | enter | 13 |
示例：
<!DOCTYPE html><html><head><title>键盘事件keycode</title></head><body>left up right down<br />ctrl + up ctrl + down<br />ctrl + 1 ctrl + 2 ctrl + 3<br />a ctrl + a ctrl + shift + a<br /><script type="text/javascript">document.onkeydown = function (event) {event = event || window.event;bCtrlKey = event.ctrlKey;bShiftKey = event.shiftKey;switch (event.keyCode) {case 37:alert("left");break;case 38:if (bCtrlKey) {alert("ctrl+up");break;}alert("up");break;case 39:alert("right");break;case 40:if (bCtrlKey) {alert("ctrl+down");break;}alert("down");break;case 49:bCtrlKey && (alert("ctrl+1"));break;case 50:bCtrlKey && (alert("ctrl+2"));break;case 51:bCtrlKey && (alert("ctrl+3"));break;case 65:if (bCtrlKey) {if (bShiftKey) {alert("自定义");break;}alert("全选");break;}alert("a");break;case 67:bCtrlKey && (alert("复制"));break;case 86:bCtrlKey && (alert("粘贴"));break;}return false;}</script></body></html>———————————————————————————————
<script language="javascript">function keyevent(){if(event.keyCode==13)alert("#$%#%#^^%");}document.onkeydown = keyevent;</script>event.keyCode值为37﹐38﹐39﹐40对应按下的方向键分別是 左﹐上﹐右﹐下"javascript:if (event.keyCode < 45 || event.keyCode > 57) event.returnValue = false;");if(event.keycode==13)就代表按下的是回车键盘"javascript:if (event.keyCode > 45 && event.keyCode < 57) event.returnValue = false;");----------------------------------------------------------------------------------------------
<参考：http://lfsp.btwlo.com/keycode.html & http://www.cnblogs.com/xingqiba/archive/2012/06/12/2546148.html & http://www.cnblogs.com/kuikui/archive/2012/02/09/2343645.html>
