text文本框数字相加

Question

<script>
function sumNum(obj){
var trObj=obj.parentNode.parentNode;
var number1 = isNaN(parseInt(trObj.childNodes[1].firstChild.value,10))?0:parseInt(trObj.childNodes[1].firstChild.value,10); 
var number2 = isNaN(parseInt(trObj.childNodes[2].firstChild.value,10))?0:parseInt(trObj.childNodes[2].firstChild.value,10); 
var number3 = isNaN(parseInt(trObj.childNodes[3].firstChild.value,10))?0:parseInt(trObj.childNodes[3].firstChild.value,10); 
var number4 = isNaN(parseInt(trObj.childNodes[4].firstChild.value,10))?0:parseInt(trObj.childNodes[4].firstChild.value,10); 
trObj.childNodes[5].firstChild.value = number1 + number2  + number3 + number4;
}
</script>将所有onpropertychange="sumNum()"换成onpropertychange="sumNum(this)"