js类中私有变量与私有方法的实现

今天详细了解了下这方面的，算是做个记录

es5中实现

主要还是使用闭包实现，Object.defineProperty不能实现。

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var People = (function(){
	function privateFunc(){
		console.log('privateFunc')
	}
	var privateVar = 'privateVar';
	function People(){
		this.publicVar = '1';
	}
	People.prototype.publicFunc = function(){
		privateFunc.call(this);
	}
	return People;
})()
var people = new People();
Object.keys(people);		//['publicVar']
people.publicFunc();		//'private test'

es6中实现

采用闭包+symbol实现

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var People = (function(){
	var s1 = Symbol('privatekey');
	var s2 = Symbol('privatekey')
	class People{
		constructor(){
			this[s1] = () => {console.log('privateFunc')};
			this[s2] = 'privateVar';
		}
		publicFunc(){
			console.log(this[s1]());
			console.log(this[s2]);
		}
	}
	return People;
})()
var people = new People();
Object.keys(people);		//['publicVar']
people.publicFunc();		//'private test'

symbol是es新添加的一种数据类型（之前有六种：null, undefined, 数字，字符串，布尔，对象），每次都能生成一个唯一不同的值。它有一个很重要的特点：它虽然不是私有属性，但是不会出现在for…in,for…of循环中，也不会被Object.keys()、Object.getOwnPropertyNames()返回。所以直接定义在this上并不会被枚举到。
但是这也不是万无一失，有两个api可以查询到symbol属性：Object.getOwnPropertySymbols和Reflect.ownKeys。但是这基本能满足需求了

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people[Object.getOwnPropertySymbols(people)[0]]();		//'privateFunc'
people[Object.getOwnPropertySymbols(people)[1]];		//'privateVar'