Object oriented programming

object oriented programming (OOP) is a programming pardigm where data is dealt with in a similar fashion to objects in a real world. A simple example would be cars. Each car has similar qualities like color, model, make, these are called properties. Each car also functions in a similar way and can do things like start, brake, accelerate, steer, etc. these are know as methods but can also be referred to as functions.

Using the information above here is a simple example of what a car object would look like in javascript. Creating an object using this method is called writing an object literal

var civic = {
  make: 'Honda',
  model: 'Civic',
  color: 'blue',
  gallonsOfGas: 5,
  speed: 0,

  accelerate: function(){
    this.speed += 1;
    this.gallonsOfGas -= 0.01;
  },

  brake: function(){
    this.speed -= -1;
  }
}

Another way of creating an object is using the new keyword to first create or instantiate the object, then adding values using dot notation or passing the key like so civic['model'] = 'Civic';

var civic = new Object();

civic.color = 'red';
civic['model'] = 'Civic'; // alternate syntax

Writing this information out can be tedious, what if we had a quick way to enter all of this information, and let the computer take care of constructing the object? Fortunately we do! This is what's known as a constructor function.

function Car(make, model, color, gallonsOfGas){
  this.make = make;
  this.model = model;
  this.color = color;
  this.gallonsOfGas = gallonsOfGas;
  this.speed = 0;
  this.accelerate = function(){
    this.speed += 1;
    this.gallonsOfGas -= 0.01;
  },

  this.brake = function(){
    this.speed -= -1;
  }
}

Then we can easily create a new Car using the following.

var corvette = new Car('Chevrolet', 'Corvette', 'red', '0');

Finally, we access these properties using dot notation, and we access the methods the same way, but to use the method we need to call them by adding () to the end.

corvette.speed; // returns 0
corvette.accelerate(); // returns undefined, but adds 1 to speed
corvette.speed // now returns 1