JavaScript计算加减乘除

//加法函数
function jiafa(a,b){
	var a=parseInt(document.getElementById("number1").value); //parseInt()把文本转为Int类型
	var b=parseInt(document.getElementById("number2").value);
	var c=a+b; //减法、乘法、除法同理
	document.getElementById("sum1").value=c;
	}
</script>

<p>
<input type="text" id="number1" />&nbsp+ <input type="text" id="number2"  />  = <input type="text" id="sum1"/>  <input type="button" value="计算" onclick="jiafa()" />
</p>