Definition
Main OOP Concepts
- Encapsulation
- It's the process of combining data and functions into a single unit called class
- Abstraction
- It's the concept of exposing the relevant details of an object to the outside world while keeping the unnecessary details of an object hidden to the outside world.
- Inheritance
- It's like using the structure and behaviour of a super class in a subclass.
- Polymorphism
- In polymorphism what we do is, we change the structure and behavior of the parents class from child class. There are two ways to achieve this.
- Overriding - Dynamic binding / Run-Time binding / Late binding (Different class)
- Overloading - Static binding / Compile time binding / Early binding (Same Class)
Encapsulation
Private Properties
All properties of an object are public. you can make variables private easily by declaring them inside the constructor.
function Person(name,age,ssn){
this.name = name;
this.age = age;
//making social_security_no variable private
var social_security_no = ssn;
// 2324352212 this works since we are acccessing it inside the function
console.log(social_security_no)
}
var person = new Person("Ajith",24,"2324352212");
console.log(person.name); //Ajith
console.log(person.age); //24
console.log(person.social_security_no); //undefined
//let's use the prototype object to access ssn
Person.prototype.getSSN = () => {
return this.social_security_no;
}
console.log(person.getSSN()); //undefined
Getters and Setters
Getters and Setters are used to set and get private variables defined inside a function in javascript. There are few ways to create getters and setters in javascript. Most ways are deprecated after ES5.
Modern Approach( ECMA ^5.1)
function Circle(){
//private radius
var _radius = 0;
}
//Getters and Setters
Circle.prototype = {
set setRadius(radius){
_radius = radius;
},
get getRadius(){
return _radius;
},
get getArea(){
return Math.PI * _radius * _radius;
}
};
var circ = new Circle();
circ.setRadius = 10;
// undefined , can't access a private variable.
// undefined , can't access a private variable.
console.log(circ._radius);
console.log(circ.getArea.toFixed(2)); //314.16
circ.setRadius = 100;
console.log(circ.getArea.toFixed(2)); //31415.93
Modern Approach 2 (ECMA 5.0)
function Circle(){
var radius = 0;
}
Object.defineProperty(Circle.prototype,"Radius",{
get: () => {
return this.radius;
},
set : (radius) => {
this.radius = radius;
}
});
Object.defineProperty(Circle.prototype,"Area",{
get: () => {
return this.radius * this.radius * Math.PI;
}
});
var circ = new Circle();
circ.Radius = 10;
// undefined , can't access a private variable.
console.log(circ.radius);
console.log(circ.Area);
Deprecated Approaches
- Object.__defineGetter__(prop, func)
- Object.__defineGetter__.call(Circle.prototype,"getArea",function(){return area;});
- Object.__defineSetter__(prop, func)
- Object.__defineSetter__.class(Circle.prototype,"setRadius",function(radius){this.radius = radius;});
In a nutshell, encapsulation is the process of combining data and functions into a single unit called class. The function consists of private variables. Getters and Setters are used to get and set values for these private members. Look at the given image below.
 |
| Encapsulation |
