能否解释下function里面的功能
<!DOCTYPE html>
<html>
<head>
<title> 事件</title>
<script type="text/javascript">
function count(select){
var num1=parseInt(document.getElementById("txt1").value);
var select=document.getElementById("select").value;
var num2=parseInt(document.getElementById("txt2").value);
var result;
switch(select){
case "*":
result=num1*num2;
break;
case "/":
result=num1/num2;
break;
case "+":
result = num1+num2;
break;
case "-":
result = num1-num2;
break;
default:
result="计算错误";
}
document.getElementById( "fruit").value=parseInt(result);
}
</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>
