有大佬吗，救救孩子，运行不了
<!DOCTYPE html>
<html>
<head>
<title> 事件</title>
<script type="text/javascript">
function count(){
var txt1 = document.getElementById("txt1").value;//获取第一个输入框的值
var txt2 = document.getElementById("txt2").value; //获取第二个输入框的值
var info = document.getElementById("select").value;//获取选择框的值
var txt3 = "";
switch(info){
case:'+':
txt3 = parseFloat(txt1)+parseFloat(txt2);
break;
case:'-':
txt3 = parseFloat(txt1)-parseFloat(txt2);
break;
case:'*':
txt3 = parseFloat(txt1)*parseFloat(txt2);
break;
case:"/":
txt3 = parseFloat(txt1)/parseFloat(txt2);
break;
default:
document.write("无此功能");
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
document.getElementById('fruit').value = txt3; //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>
把这四个：去掉
