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JS constructor Method

In JavaScript, the constructor method is a special method that is automatically called when a new instance of a class or an object is created. It’s used to initialize the newly created object with default values or to perform any necessary setup tasks.

Usage in ES6 Classes:

  • In ES6, the constructor method is used within class definitions to define the initialization logic for objects created with the class.
  • It’s a reserved keyword and must be spelled exactly as constructor.
  • The constructor method is optional. If not provided, a default constructor is used implicitly.
					class ClassName {
    constructor(/* constructor parameters */) {
        // Constructor logic



  • The constructor method can accept parameters, which are passed when creating new instances of the class. These parameters are used to customize the initialization of each instance.
					class Person {
    constructor(name, age) {
        this.name = name;
        this.age = age;
    greet() {
        console.log(`Hello, my name is 
        ${this.name} and I am ${this.age} years old.`);

// Creating instances of the Person class
let person1 = new Person("Alice", 30);
let person2 = new Person("Bob", 25);

// Output: Hello,
my name is Alice and I am 30 years old.
// Output: Hello, my name is Bob and
I am 25 years old.


Initialization Logic:

  • Inside the constructor method, you can perform any necessary setup tasks such as initializing instance properties, setting default values, or calling other methods.

Automatically Called:

  • The constructor method is automatically called when you use the new keyword to create a new instance of a class or an object.

Return Value:

  • The constructor method does not return anything explicitly. Its main purpose is to initialize the newly created object.

Use Cases:

  • Initializing instance properties with default values.
  • Performing setup tasks that need to be done whenever a new object is created.