1.

What are classes in javascript?

Answer»

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. An error will be thrown if the strict mode rules are not followed.


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