<!DOCTYPE html>
<html>
<head>
<title> 事件</title>
<script type="text/javascript">
function count()
{
var firstkey = document.getElementById("txt1");
//获取第一个输入框的值
var secondkey = document.getElementById("txt2");
//获取第二个输入框的值
//获取选择框的值
var calculate = document.getElementById("select");
//获取通过下拉框来选择的值来改变加减乘除的运算法则
switch(calculate)
{
case "+":
var result = parseInt(firstkey) + parseInt(secondkey);
break;
case "-":
var result = parseInt(firstkey) - parseInt(secondkey);
break;
case "*":
var result = parseInt(firstkey) * parseInt(secondkey);
break;
case "/":
var result = parseInt(firstkey) / parseInt(secondkey);
break;
}
//设置结果输入框的值
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>
你的获取值代码中的.value没加上