现在有两个变量，分别是a = 3, b = 4，那么我们不用第三个变量来调换a和b的值。
<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<title>变量、作用域</title>
</head>
<body>
<script type="text/javascript">
var a = 3, b = 4;
/*此处写代码*/
a=a+b;
b=a-b;
a=a-b;
</script>
</body>
</html>