实时多个文本框的数字相加并把值显示到另一个文本框

<div id="toadd">
<input type="text" /><input type="text" /><input type="text" /><input type="text" /><input type="text" />
</div>
<input type="text" id="result" />

<input type="button" value="相加" onclick="runadd()"/>

<script>
runadd = function(){
    var v = document.getElementById("toadd").getElementsByTagName("input");
    var sum = 0;
    for (var i=0;i<v.length ;i++ )
    {
        sum += (!v[i].value ? 0 : parseFloat(v[i].value));
    }
    document.getElementById("result").value = sum;
}
</script>