ES6ClassWithPrivateProps.js

/**
 * How to declare a real private members in a JavaScript class?
 * 
 * Prerequisities
 * --------------
 * 1. This is a node module, as it's wrapped in a closure (Module Pattern).
 *    e.g. var XXX = (function() { ... })();
 * 2. Need ES6 support.
 * 
 * Solution
 * --------
 * Because Keys of WeakMaps are of the type Object only. Primitive data types as
 * keys are not allowed (e.g. a Symbol can't be a WeakMap key). We can use it to
 * store private members.
 */

let pv = new WeakMap();

export default class TheClass {

  constructor() {
    // Private members /////////////////////////////////////////////////////////
    pv.set(this, {
      props1: 0,
      props2: '456',
      props3: '789'
    });
    // Public members //////////////////////////////////////////////////////////
    this.pub1 = 123;
    this.pub2 = 456;
  }

  /**
   * Public function 1.
   */
  publicFn1() {
    // Alter the private members by increasing it by one.
    ++pv.get(this).props1;
    console.log(pv.get(this).props1);
  }

}