What are classes in javascript?

 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("Vijay", 354, "6th", "A");
student1.getDetails();
// Returns Name: Vijay, 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.