js键盘上下左右键如何触发function

<script type="text/javascript">

function jumpPage() {

if (event.keyCode==37)//左

fun_a();

if (event.keyCode==38)//上

fun_b();

if (event.keyCode==39)//右

fun_c();

if (event.keyCode==40)//下

fun_d();

}



function fun_a(){

window.alert('你按下了左')

}

function fun_b(){

window.alert('你按下了上')

}

function fun_c(){

window.alert('你按下了右')

}

function fun_d(){

window.alert('你按下了下')

}

document.onkeydown=jumpPage;

</script>



HTML code
<table
width="100%" border="1"
cellspacing="1"
cellpadding="0"
id=table>
<tr
id="lineone" style="background-color:#00cccc;">
<td
id=aa height="23"> </td>
<td
id=aa >按向下键</td>
<td
id=cc >按向下键</td>
<td
id=dd >按向下键</td>
<td
id=ee >按向下键</td>
</tr>
<tr
id="linetwo" tyle="background-color:#ffffff;">
<td
id=a height="23"> </td>
<td
id=b >按向上键</td>
<td
id=c >按向上键</td>
<td
id=d >按向上键</td>
<td
id=e >按向上键</td>
</tr></table><script
language="javascript">
function
keyDown(e) {
var iekey=event.keyCode; action(iekey); } document.onkeydown
=
keyDown; function
action(iekey) {
if(iekey==40)
{ lineone.style.backgroundColor
= ""; linetwo.style.backgroundColor
=
"#00cccc"; }
if(iekey==38)
{ lineone.style.backgroundColor
= "#00cccc";
linetwo.style.backgroundColor
= ""; } }
</script><input
name="id"
type="hidden" id="id"
value="1"
/>