<!DOCTYPE html>
<html>
<head>
<title> 事件</title>
<script type="text/javascript">
function count(){
//获取第一个输入框的值
var a = document.getElementById('txt1').value;
//获取第二个输入框的值
var b = document.getElementById('txt2').value;
//获取选择框的值
var c = document.getElementById('select').value;
var result = "";
//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(c){
case '+':
result = parseInt(a) + parseInt(b);
break;
case '-':
result = parseInt(a) - parseInt(b);
break;
case '*':
result = parseInt(a) * parseInt(b);
break;
default:
result = parseInt(a) / parseInt(b);
}
//设置结果输入框的值
result = document.getElementById('fruit').value;
}
</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>
result = document.getElementById('fruit').value;
替换成：
document.getElementById('fruit').value=result;