<!DOCTYPE html>
<html>
<head>
<title> 事件</title>
<script type="text/javascript">
function count(){
var value3;
var value1=parseInt(document.getElementById("txt1").value);//获取第一个输入框的值
var value2=parseInt(document.getElementById("txt2").value);//获取第二个输入框的值
var select1=document.getElementById("select").value;//获取选择框的值
console.log(value1);
console.log(value2);
switch (select1){
case "+":
value3=value1+value2;
break;
case "-":
value3=value1-value2;
break;
case "*":
value3=value1*value2;
break;
case "/":
value3=value1/value2;
break;
}//获取通过下拉框来选择的值来改变加减乘除的运算法则
console.log(value3);
document.getElementById("fruit").value=value3;//设置结果输入框的值
}
</script>
</head>
<body>
<input type=‘text‘ id=‘txt1‘ />
<select id=‘select‘>
<option value=‘+‘>+</option>
<option value="-">-</option>
<option value="*">*</option>
<option value="/">/</option>
</select>
<input type=‘text‘ id=‘txt2‘ />
<input type=‘button‘ value=‘ = ‘ onclick="count()"/> <!--通过 = 按钮来调用创建的函数，得到结果-->
<input type=‘text‘ id=‘fruit‘ />
</body>
</html>
原文：http://www.cnblogs.com/jianxingjianyuan/p/6435153.html