Question

76

How to work with private variables in ES6?

rated 0 times [ 82] [ 6] / answers: 1 / hits: 11512 / 9 Years ago, tue, december 22, 2015, 12:00:00

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(){



    }

}

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

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;

    }

}

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emiliano

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3 Years ago

answered 9 Years ago donaldcristianl · Accepted Answer

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

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

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()

The best you could do is to use those techniques with Symbols or WeakMaps

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;

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.