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What are classes in javascript?

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Introduced in the ES6 version, classes are nothing but syntactic sugars for constructor functions.

They provide a new way of declaring constructor functions in javascript.

Below are the examples of how classes are declared and used:

// Before ES6 version, using constructor functions

function Student(name,rollNumber,grade,section){

  this.name = name;

  this.rollNumber = rollNumber;

  this.grade = grade;

  this.section = section;

}

// Way to add methods to a constructor function

Student.prototype.getDetails = function(){

  return 'Name: ${this.name}, Roll no: ${this.rollNumber}, Grade: ${this.grade}, Section:${this.section}';

}

let student1 = new Student("Vivek", 354, "6th", "A");

student1.getDetails();

// Returns Name: Vivek, Roll no:354, Grade: 6th, Section:A

// ES6 version classes

class Student{

  constructor(name,rollNumber,grade,section){

    this.name = name;

    this.rollNumber = rollNumber;

    this.grade = grade;

    this.section = section;

  }

  // Methods can be directly added inside the class

  getDetails(){

    return 'Name: ${this.name}, Roll no: ${this.rollNumber}, Grade:${this.grade}, Section:${this.section}';

  }

}

let student2 = new Student("Garry", 673, "7th", "C");

student2.getDetails();

// Returns Name: Garry, Roll no:673, Grade: 7th, Section:C

Key points to remember about classes:

Unlike functions, classes are not hoisted. A class cannot be used before it is declared.

A class can inherit properties and methods from other classes by using the extend keyword.

All the syntaxes inside the class must follow the strict mode(‘use strict’) of javascript. Error will be thrown if the strict mode rules are not followed.
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