JavaScript Classes

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JavaScript Classes


ECMAScript 2015, also known as ES6, introduced JavaScript Classes.
JavaScript Classes are templates for JavaScript Objects.

JavaScript Class Syntax
Use the keyword class to create a class.
Always add a method named constructor():

Syntax

class ClassName {
  constructor() { ... }
}



Example

class Car {
  constructor(name, year) {
    this.name = name;
    this.year = year;
  }
}


The example above creates a class named "Car".
The class has two initial properties: "name" and "year".

A JavaScript class is not an object.
It is a template for JavaScript objects.


Using a Class
When you have a class, you can use the class to create objects:

Example

const myCar1 = new Car("Ford", 2014);
const myCar2 = new Car("Audi", 2019);


Try it Yourself »


The example above uses the Car class to create two Car objects.

The constructor method is called automatically when a new object is created.


The Constructor Method
The constructor method is a special method:

It has to have the exact name "constructor"
It is executed automatically when a new object is created
It is used to initialize object properties

If you do not define a constructor method, JavaScript
will add an empty constructor method.








Class Methods
Class methods are created with the same syntax as object methods.
Use the keyword class to create a class.
Always add a constructor() method.
Then add any number of methods.

Syntax

class ClassName {
  constructor() { ... }
  method_1() { ... }
  method_2() { ... }
  method_3() { ... }
}


Create a Class method named "age", that returns the Car age:

Example

class Car {
  constructor(name, year) {
    this.name = name;
    this.year = year;
  }  age() {
    const date = new Date();
    return date.getFullYear() - this.year;
  }}
const myCar = new Car("Ford", 2014);
document.getElementById("demo").innerHTML =
"My car is " + myCar.age() + " years old.";


Try it Yourself »


You can send parameters to Class methods:

Example

class Car {  constructor(name, year) {   
this.name = name;    this.year = year;  } 
age(x) {    return x - this.year;  }}
const date = new Date();
let year = date.getFullYear();const myCar = new
Car("Ford", 2014);document.getElementById("demo").innerHTML="My car is
" + myCar.age(year) + " years old.";

Try it Yourself »




Browser Support
The following table defines the first browser version with full support for
Classes in JavaScript:










Chrome 49
Edge 12
Firefox 45
Safari 9
Opera 36


Mar, 2016
Jul, 2015
Mar, 2016
Oct, 2015
Mar, 2016




You will learn a lot more about JavaScript Classes later in this tutorial.













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Reference: https://www.w3schools.com/js/js_classes.asp

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