Javascript ES6 Class example

ES6 Class Basics

JavaScript’s prototypal inheritance model can appear confusing to developers with an understanding of the classical inheritance used in languages such as C++, C#, Java and PHP. JavaScript classes are primarily syntactical sugar, but they offer more familiar object-oriented programming concepts.
A class is a template which defines how objects of that type behave. The following Animal class defines generic animals (classes are normally denoted with an initial capital to distinguish them from objects and other types):

class Animal {

  constructor(name = 'anonymous', legs = 4, noise = 'nothing') {

    this.type = 'animal';
    this.name = name;
    this.legs = legs;
    this.noise = noise;

  }

  speak() {
    console.log(`${this.name} says "${this.noise}"`);
  }

  walk() {
    console.log(`${this.name} walks on ${this.legs} legs`);
  }

}

Class declarations execute in strict mode; there’s no need to add 'use strict'.
A constructor method is run when an object of this type is created, and it typically defines initial properties. speak() and walk() are methods which add further functionality.
An object can now be created from this class with the new keyword:

const rex = new Animal('Rex', 4, 'woof');
rex.speak();          // Rex says "woof"
rex.noise = 'growl';
rex.speak();          // Rex says "growl"

Getters and Setters

Setters are special methods used to define values only. Similarly, Getters are special methods used to return a value only. For example:

class Animal {

  constructor(name = 'anonymous', legs = 4, noise = 'nothing') {

    this.type = 'animal';
    this.name = name;
    this.legs = legs;
    this.noise = noise;

  }

  speak() {
    console.log(`${this.name} says "${this.noise}"`);
  }

  walk() {
    console.log(`${this.name} walks on ${this.legs} legs`);
  }

  // setter
  set eats(food) {
    this.food = food;
  }

  // getter
  get dinner() {
    return `${this.name} eats ${this.food || 'nothing'} for dinner.`;
  }

}


const rex = new Animal('Rex', 4, 'woof');
rex.eats = 'anything';
console.log( rex.dinner );  // Rex eats anything for dinner.

Child or Sub-Classes

It’s often practical to use one class as the base for another. If we’re mostly creating dog objects, Animal is too generic, and we must specify the same 4-leg and “woof” noise defaults every time.
A Dog class can inherit all the properties and methods from the Animal class using extends. Dog-specific properties and methods can be added or removed as necessary:

class Dog extends Animal {

  constructor(name) {

    // call the Animal constructor
    super(name, 4, 'woof');
    this.type = 'dog';

  }

  // override Animal.speak
  speak(to) {

    super.speak();
    if (to) console.log(`to ${to}`);

  }

}

super refers to the parent class and is usually called in the constructor. In this example, the Dog speak() method overrides the one defined in Animal.
Object instances of Dog can now be created:

const rex = new Dog('Rex');
rex.speak('everyone');      // Rex says "woof" to everyone

rex.eats = 'anything';
console.log( rex.dinner );  // Rex eats anything for dinner.

Static Methods and Properties

Defining a method with the static keyword allows it to be called on a class without creating an object instance. JavaScript doesn’t support static properties in the same way as other languages, but it is possible to add properties to the class definition (a class is a JavaScript object in itself!).
The Dog class can be adapted to retain a count of how many dog objects have been created:










REF:
https://www.sitepoint.com/javascript-private-class-fields/