Classes

defining

• have a name
• can extend another class
• can define a constructor method
• can define properties
• can define methods
• can define accessor methods
  • getters and setters

Classes

have a name

class Rocket {
  
}

Classes

can define a constructor method

class Rocket {
  constructor( model, destination ){
    
  }
}

Classes

can define properties

fuel is a public properties

_launchCount, _model and _destination are private

class Rocket {

  fuel = 100;
  _launchCount = 0;

  constructor( model, destination ){
    this._model = model;
    this._destination = destination;
  }
}

Classes

can define accessor methods
(getters and setters) to access private properties

class Rocket {

  fuel = 100;
  _launchCount = 0;

  constructor( model, destination ){
    this._model = model;
    this._destination = destination;
  }

  get model(){
    return `Rocket Model: ${this._model}`;
  }

  set model( model ){
    if( typeof(model) === 'string' ){
      this._model = model;
    }else{
      throw new TypeError('Rocket.model must be a string');
    }
  }
}

Classes

can define accessor methods
(getters and setters) to access private properties

class Rocket {

  fuel = 100;
  _launchCount = 0;

  constructor( model, destination ){
    this._model = model;
    this._destination = destination;
  }

  get launchCount(){
    return _launchCount;
  }

  set launchCount( launchCount ){
    if( typeof(launchCount) === 'number' ){
      this._launchCount = launchCount;
    }else{
      throw new TypeError('Rocket.launchCount must be a number');
    }
  }
}

Classes

can define methods

class Rocket {

  fuel = 100;
  _launchCount = 0;

  constructor( model, destination ){
    this._model = model;
    this._destination = destination;
  }

  launch(){
    this._launchCount++;
    console.log('to the moon');
  }

}

Class Inheritence

• extend superclass properties and methods
• defines it's own constructor method
  • must invoke it's superclass constructor
    before using the `this` keyword
• can override inherited methods

Define a Superclass

class Vehicle {
  constructor( destination ){
    this._destination = destination;
  }
  
  get destination(){
    return this._destination;
  }
  set destination( destination ){
    if( typeof(destination) === 'string' ){
      this._destination = destination;
    }else{
      throw new TypeError('Vehicle.destination must be a string');
    }
  }
}

Extend the Superclass

class Rocket extends Vehicle{
  
  constructor( model, destination ){
    super( destination );
    this._model = model;
  }

}

// Vehicle is not defined

Import the Superclass definition

import Vehicle from './Vehicle';

class Rocket extends Vehicle{
  
  constructor( model, destination ){
    super( destination );
    this._model = model;
  }

}

Creating Objects

Instances of Classes

• use the new keyword to create an instance

• the constructor method is invoked on creation

  • constructor arguments can be passed in

new Rocket('Raccoon', 'The Moon');

• Classes cannot be invoked like normal functions

Rocket('Raccoon', 'The Moon');
// Cannot call a class as a function

Instance Properties

• assign the instance to a variable

• use dot notation or bracket notation to access properties

var raccoon = new Rocket('Raccoon', 'The Moon');
raccoon.fuel;
raccoon['fuel'];

Accessor Methods

• access properties through getter and setter methods as if they normal are properties

var raccoon = new Rocket('Raccoon', 'The Moon');
raccoon.model; // 'Rocket Type: Raccoon'
raccoon.model = 'Lunar Raccoon';
raccoon['model']; // 'Rocket Type: Lunar Raccoon'
raccoon['model'] = 404; // Rocket.model must be a string

• assigning a new property to an object will implicitly invoke it's set accessor method 

Instance Methods

• invoke instance methods normally

• use dot notation or bracket notation

var raccoon = new Rocket('Raccoon', 'The Moon');
raccoon.launch(); // 'to the moon'
raccoon['launch'](); // 'to the moon'

Inherited properties and methods

from the superclass

var raccoon = new Rocket('Raccoon','The Moon');
raccoon.destination; // The Moon
raccoon.destination = 404; // Vehicle.destination must be a string

Checking Instance Type

• use instanceof

var raccoon = new Rocket('Raccoon', 'The Moon');
raccoon instanceof( Rocket )  // true
raccoon instanceof Rocket     // true
raccoon instanceof( Vehicle ) // true
raccoon instanceof Vehicle    // true