如何让函数定义的参数值都不同

Question

div的onmouseover事件加上showdiv方法，但参数p的值总是5，有什么办法实现是1,2,3,4,5呢
<div id='a1'>a1</div>
<div id='a2'>a2</div>
<div id='a3'>a3</div>
<div id='a4'>a4</div>
<div id='a5'>a5</div>
<script type="text/javascript">
for(var i=1;i<=5;i++){
var aa = document.getElementById('a'+i);
var p = i;
aa.onmouseover = function(){showdiv(p);};
//alert(aa);
}
function showdiv(v){
alert(v);
}
</script>

Answer 1

<div id='a1'>a1</div>
<div id='a2'>a2</div>
<div id='a3'>a3</div>
<div id='a4'>a4</div>
<div id='a5'>a5</div>
<script type="text/javascript">
window.onload = function() {
for(var i=1;i<=5;i++){
var aa = document.getElementById('a'+i);
aa.onmouseover = (function(j){
return function(){showdiv(j);};
})(i);
//alert(aa);
}
}
function showdiv(v){
    alert(v);
}
</script>