constructorPattern.md

Constructor pattern

Constructors are used to create specific types of objects.

In JS, an object can be created 3 different ways:

var newObject = {};

var newObject = Object.create(Object.prototype);

var newObject = new Object();

4 ways to add keys and values to an object:

// 1
newObject.newKey = 'hello';

// 2
newObject['newKey'] = 'hello';

// 3
Object.defineProperty(newObject, 'newKey', {
  value: 'hello',
  writable: true,
  enumerable: true,
  configurable: true
})

// 4
Object.defineProperties(newObject, {
  'newKey' : {
    value: 'hello',
    writable: true
  }
});

Example of constructor pattern in JS:

function Car(year, model){
  this.year = year;
  this.model = model;

  this.toString = function(){
    return this.model + " was released in " + this.year;
  }
}

var delorean = new Car(1975, "DeLorean");

console.log(delorean.toString());

The above example makes inheritance difficult and it causes to redefine the function toString for every object using the Car constructor. This function should instead be shared by all instances of the Car type.

Constructors with prototype

function Car(year, model){
  this.year = year;
  this.model = model;
}

Car.prototype.toString = function(){
  return this.model + "was released in " + this.year;
}

var delorean = new Car(1975, "DeLorean");
console.log(delorean.toString());

In the above example, the method toString will now be shared across all instances of the Car type.