为什么不显示结果
<!DOCTYPE html>
<html>
<head>
<title> 事件</title>
<script type="text/javascript">
function count(){
var num1=parseInt(document.getElementById('txt1'));
var num2=parseInt(document.getElementById('txt2'));
var opt=document.getElementById('select');
var result="";
switch(opt){
case "+":
result=num1+num2;
break;
case "-":
result=num1-num2;
break;
case "*":
result=num1*num2;
break;
case "/":
result=num1/num2;
}
document.getElementById('fruit').value=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>点了按钮后面结果没反应
