[ES2015] Classes in JavaScript

ES2015 / ES6 Classes in JavaScript

Classes in JS don’t give JS an OO nature, JS remains Prototypal. Classes introduced in ES6 are mainly syntax sugar.

"use strict";

class User{
  // Constructor
  // takes any values/attr you want to set
  constructor(username, email, password) {
    this.username = username // Whatever username we passed in is now this Class's (instance) username
    this.email = email
    this.password = password

  static countUsers () {
    console.info('There are 50 users')

  // Methods
  register() {
    console.log(`${this.username} is now registered`)

// Instantiate the class
let Bob = new User('bob', 'bob@bobby.com', '123supersecretpass')

// Call a method 
Bob.register() // bob is now registered

class Memeber extends User {
  constructor(username, email, password, memberPackage) {
    super(username, email, password)
    this.package = memberPackage

  getPackage() {
    console.info(`${this.username} is subscribed to the ${this.package} package`)

let mike = new Member('mike', 'mike@email.com', 'pass123', 'Standard')

mike.register() // mike is now registereds
mike.getPackage() // mike is subscribed to the Standard package


Constructors are methods that’ll run when your class is instantiated. They can take parameters. You can then set these params (passed in values) and assign them to class properties.


Methods are functions that belong to a class. You can call them on an instance of a class, like so:

Bob.register() // bob is now registereds

You can also have static methods. Whatever. Static methods can be called without having to instantiate a class, like this:

User.countUsers() // There are 50 users


You can extend existing classes to create new classes. super constructor calls (functions etc.) on theconstructor in the parent class. super needs to be called before you can use the this keyword.

class Member extends User {}

Classes vs Functions?

You should create a class whenever you have code that needs to be self-aware or keep something in memory. Whatever that means.