读一个变量的值

Question

var idname="PN";
var a=document.getElementById(idname).value;
怎么获取不到idname的值?请高人帮我解决，谢谢!

Answer 1

<Script language="javascript">function test()
{
var idname="PN";
var a=document.getElementById(idname).value;
alert(a);}
</Script>
<input id="PN"  type="text" value="DSDSADSA">
<input type="submit"  value="ssssss"  onClick="test()">没有问题啊