成功了，最后结果能返回到第三个文本框
<!DOCTYPE html>
<html>
<head>
<title> 事件</title>
<script type="text/javascript">
function count(){
var num1,num2,fuhao,jieguo;
var fuhao=document.getElementById('select').value;
var num1=parseInt(document.getElementById('txt1').value);
var num2=parseInt(document.getElementById('txt2').value);
switch(fuhao){
case "+" :
jieguo=num1+num2;
break;
case "-" :
jieguo=num1-num2;
break;
case "*" :
jieguo=num1*num2;
break;
case "/" :
jieguo=num1/num2;
break;
}
document.getElementById('fruit').value = jieguo;
alert(jieguo);
}
</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' value="结果"/>
</body>
</html>
