Greycampus

Fundamentals

First, let us define some fundamentals required to understand a few concepts of oops.

Classes

As a prototyping language javascript does not contain any class statement. Instead javascript uses functions as classes.

Objects

Javascript has two types of objects, Core objects, and User-defined objects

Core objects are a list of predefined objects in the javascript core; these functions have a global scope, i.e., they can be used anywhere in the project.

Example: Math object

User-defined objects are defined using the new statement. User-defined objects cannot use the same names used by the core objects of javascript.

Object Properties

An object-oriented programming language provides developers with four capabilities:

Encapsulation
Inheritance
Polymorphism
Aggregation

Inheritance

Inheritance is the ability of a class(class A) to acquire the properties another class(class B). Here class A is referred to as the child class and class B is regarded as the parent class. The child class inherits all the methods defined in the parent.

Encapsulation

Even though the child class can use the inherited methods, it does not need to know the inner working of those methods. Unless we need to change the operation, we do not need to define the method in the child class explicitly.

Polymorphism

The ability to define different methods in different classes with the same name is 'polymorphism.' Unless the class has a parent-child relationship with another class, javascript restricts the scope of these methods to the class. Thus making polymorphism possible.

Abstraction

Abstraction is the ability of the language to hide most of the details only to show the essential features of the project. Hence, Abstraction improves the understandability and the readability of the code. We apply abstraction in java using prototypes.


    
        <script>
/*
build a class to store the data of the mobile phones with screen size,ram,company and processor along with Constructor and function to estimate cost of phone based on conditions
  samsung:7000(pr)
  moto:5999
  lenovo:4000
  nokia:6100
  est cost = pr*(scr size/4.0)+pr*(ram/1.0)+pr*(proc/1.0)+0.05*pr
Input
enter screen size(inches):5.5
enter ram (GB):3
enter company name :moto
enter processor speed(Ghz)1.8
Output
the estimated cost of your moto phone is around:37343
*/
//mobiles class
class mobiles{
    //constructor initializing the class variables
    constructor(s_size,ram,company,proc){
        this.s_size = s_size;
        this.ram = ram;
        this.company = company;
        this.proc = proc;}

    estimator(){
        var ecost;
        //cost estimator calculating the cost based on company if company not listed printing not available in our catalog
        if(this.company.toLowerCase()=='samsung' || this.company.toLowerCase()=='moto'|| this.company.toLowerCase()=='lenovo' || this.company.toLowerCase()=='nokia'){
            if(this.company.toLowerCase()=='samsung'){
                ecost = 7000*(this.s_size/4)+7000*(this.ram)+7000*this.proc+0.05*7000;}
            else if(this.company.toLowerCase()=='moto'){
                ecost = 5999*(this.s_size/4)+5999*(this.ram)+5999*this.proc+0.05*5999;}
            else if(this.company.toLowerCase()=='lenovo'){
                ecost = 4000*(this.s_size/4)+4000*(this.ram)+4000*this.proc+0.05*4000;}
            else if(this.company.toLowerCase()=='nokia'){
                ecost = 6100*(this.s_size/4)+6100*(this.ram)+6100*this.proc+0.05*6100;}
            document.write('the estimated cost of your '+this.company+' phone is around:'+String(parseInt(ecost)));}
        else{
            document.write('specified company not available in our catalog');}
        }
}
var scr = parseFloat(prompt('enter screen size(inches):'));
var ram = parseFloat(prompt('enter ram (GB):'));
var com = String(prompt('enter company name :'));
var pro = parseFloat(prompt('enter processor speed(Ghz)'));
//creating instance of mobiles
var k = new mobiles(scr,ram,com,pro);
//calling estimator function
k.estimator()

</script>
        Try


    
        <script>
/*
program to Use Function Overriding in a class.
Output
B's hello
A's GoodBye
*/
class A {
  constructor() {

  }
  m1(ab){
    document.write("A's "+ab+'<br>');
  }
}
class B extends A {
  constructor() {
    super();
  }
  m1(ab){
    document.write("B's "+ab+'<br>');
  }
}
var b = new A();
var c = new B();
//c.m1() prints hello from B
c.m1('hello');
b.m1('GoodBye');
</script>

        Try