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