如何使用ES6中的私有变量？ [英] How to work with private variables in ES6?

问题描述

在ES5中，您可以使用以下私有和公共变量来模拟类：

In ES5, you could emulate a class with private and public variables like this:

car.js

function Car() {
    // using var causes speed to be only available inside Car (private)
    var speed = 10;

    // public variable - still accessible outside Car
    this.model = "Batmobile";

    // public method
    this.init = function(){

    }
}

但是在ES6中，你不能再在构造函数之外声明vars，所以它实际上是HARDER以一种OOP方式处理类！

But in ES6, you can no longer declare vars outside the constructor, making it actually HARDER to work with classes in a OOP way!?

您可以在构造函数中使用this来声明变量，但是默认情况下它们是public的。这很奇怪，因为ES6 DOES 有一个get / set关键字！

You can declare variables in the constructor using this, but that makes them public by default. This is very weird since ES6 DOES have a get / set keyword!

class Vehicle {
    constructor(make, year) {
        // the underscore is nice, but these are still public!
        this._make = make;
        this._year = year;
    }

    // get and set can be handy, but would make more sense
    // if _make and _year were not accessible any other way!
    get make() {
        return this._make;
    }

    get year() {
        return this._year;
    }
}

推荐答案

ES6标准不提供定义私有变量的新方法。

ES6 standard does not offer a new way for defining private variables.

这是一个事实，新的ES6 类基于构造函数。

It's a fact, that new ES6 class is simply syntactic sugar around regular prototype-based constructors.

get 和 set 关键字提供了一种简单定义先前定义的ES5自定义getter和setter的方法使用 Object.defineProperty（）的描述符

get and set keywords are offering a way for simplified definition of ES5 custom getters and setters that were previously defined with a descriptor of Object.defineProperty()

最好的方法是使用符号或 WeakMaps

下面的示例使用WeakMap来存储私有属性。

The example below features the use of a WeakMap for storing private properties.

// myModule.js
const first_name = new WeakMap();

class myClass {
     constructor (firstName) {
          first_name.set(this, firstName);
     }

     get name() {
          return first_name.get(this);
     }
}

export default myClass;

我指的是由David Vujic撰写的文章什么？等待。真？不好了！ （关于ES6课程和隐私的帖子）与使用WeakMaps的想法。

I'm referring to article, written by David Vujic What? Wait. Really? Oh no! (a post about ES6 classes and privacy) with the idea of using WeakMaps.

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