怎样用js实现两个输入框中的数字相加显示在第三个输入框

<input type="text" id="num1">
<input type="text" id="num2">
<input type="text"  value="" id="sum" onclick="cal()">
<script type="text/javascript">
//test input
function cal(){
document.getElementById("sum").value=(parseInt(document.getElementById("num1").value)+parseInt(document.getElementById("num2").value));
}
</script>

<input type="text" id="num1">
<input type="text" id="num2">
<input type="text"  value="" id="sum">
<script type="text/javascript">
window.onload = function(){
var inputs = document.getElementsByTagName("input");
for(i=0;i<inputs.length;i++){
inputs[i].onblur = function(){
var add1 = document.getElementById("num1").value;
var add2 = document.getElementById("num2").value;
document.getElementById("sum").value = add1*1 + add2*1;
}
}
</script>

<input type="text" id="num1">
<input type="text" id="num2">
<input type="text"  value="" id="sum">
<script type="text/javascript">
$(function (){
$("input").blur(function (){
var sum = parseInt($("#one").val()) + parseInt($("#two").val());
$("#sum").val(sum);
})
})
</script>