<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
<title></title>
</head>
<body>
<script src="js/browser.min.js" type="text/javascript" charset="utf-8"></script>
<script type="text/javascript">
'use strict';
//const用来声明常量
const PI = 3.1415926;
//const PI = 3; //报错
//var PI; //报错
//const foo; //必须立即初始化
//const只对声明的块级作用域内有效
if(true){
const MAX = 6;
}
//alert(MAX); //MAX is not defined
var message = "hello";
var age = 25;
//不能重复声明变量
//const message = "aaa"; //报错
//let age = 26; //报错
//如果是对象或者数组，只能保证地址不变，但是变量的值可以变
const foo = {};
foo.prop = 123;
console.log(foo.prop); //123
//foo = {}//地址改变了，所以报错了
//如果真的想冻结一个对象，可以使用Object.freeze
const foo2 = Object.freeze({});
//foo2.prop = 123; //报错
//对象彻底冻结的方法，即属性也冻结
var constantize = (obj) =>{
Object.freeze(obj);
Object.keys(obj).forEach(key , value) =>{
if(typeof obj[key] === 'object'){
constantize(obj[key]);
}
}
}
//没理解这上面写的啥玩意
</script>
</body>
</html>
