<!DOCTYPE html>
<html>
<head>
<title> 事件</title>
<script type="text/javascript">
function count(){
num1 = parseFloat(document.getElementById("txt1").value)
num2 = parseFloat(document.getElementById("txt2").value)
opertor = document.getElementById("select").value
var sum;
switch (opertor) {
case "+": sum = num1 + num2; break;
case "-": sum = num1 - num2; break;
case "*": sum = num1 * num2; break;
case "/": sum = num1 / num2; break;
}
document.getElementById("fruit").value = sum;
}
</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' onclick="count()" value=' = ' /> <!--通过 = 按钮来调用创建的函数，得到结果-->
<input type='text' id='fruit' />
</body>
</html>你的加减用的了嘛？ 我的用不了是网页问题还是什么？