<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<title>计算器</title>
</head>
<body>
<input type="text" id="text1" />
<select id="xq">
<option value="+">+</option>
<option value="-">-</option>
<option value="*">*</option>
<option value="/">/</option>
</select>
<input type="text" id="text2" />
<input type="button" value="=" onclick="count()" />
<input type="text" id="jg" />
</body>
</html>
<script type="text/javascript">
function count()
{
var a=document.getElementById("text1").value;
var b=document.getElementById("text2").value;
var c=document.getElementById("xq").value;
var result="";
switch(c)
{
case"+":result=parseInt(a)+parseInt(b);
break;
case"-":result=parseInt(a)-parseInt(b);
break;
case"*":result=parseInt(a)*parseInt(b);
break;
default:result=parseInt(a)*parseInt(b);
}
document.getElementById("jg").value=result;
}
</script>
原文：http://www.cnblogs.com/crazy-zw/p/5440134.html