简单实现
<html>
<!-- 参照这个地址的实现，原理 https://www.cnblogs.com/zhizu/p/7705260.html -->
<body>
<script>
console.log(typeof window.ab);
console.log(typeof window.ac);
console.log(document.getElementsByTagName('body')[0].innerHTML);
// 下面正则，最后eval http://blog.csdn.net/xundh/article/details/48153121
</script>
<script>
ab = 1;
var ac = 3;
console.log(666);
</script>
</body>
</html>