JavaScript classes

JavaScript doesn’t have classes. Classes can be only simulated using functions.

The approach to achieving this is by defining a JavaScript function where we then create an object using the new keyword. This can be used to define new properties and methods for the object as follows:

// Album "class" example 1
function Album( name , year) {
  this.name = name; 
  this.year = year;
 
  this.getInfo = function () {
    return this.name + " " + this.year;
  };
}

var album = new Album("Hello", 2016);
console.log( album.getInfo() );

or one another way to do the same, but just a touch different:

// Album "class" example 2
function Album( name , year) {
  this.name = name; 
  this.year = year; 
}

Album.prototype.getInfo = function(){
  return this.name + " " + this.year;
}

var album = new Album("Hello", 2016);
console.log( album.getInfo() );

The different approach is: we use Album.prototype or Object.prototype to define the new function inside of the object. We can refer to the prototype as to the object constructor function. And we can use prototype again and again to add new functions to the object if we wish. In the first approach we defined function getInfo inside of the function Album representing the object.

However, this is not all, the equivalent to the previous would be:

// Album "class" example 3
var album = {
  name : "Hello", 
  year : 2016, 
  getInfo : function () {
    return this.name + " " + this.year;
  };
};

anytime we could say:

album.name="Good bye";

and call

album.getInfo();

We can say write something a bit different:

// Album "class" example 4
var album = new function(){
  this.name = "Hello"; 
  this.year = 2016; 
  this.getInfo = function () {
    return this.name + " " + this.year;
  };
};

console.log( album.getInfo() );

All these are small differences, and provide us a way to create objects in JavaScript from so called classes.

JavaScript (ECMAScript=ES) may be confusing for the developers that used to work with classes at first, but then JavaScript uses objects only and achieves the object creation using functions from objects (prototypes).