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JavaScript Object Prototype


Object is Class. Almost everything in JavaScript is Object.

All JavaScript values, except premitives, are object.

Object Properties

Named value in JavaScript objects are called properties. example:

const person = {
    name: 'Jon',
    age: 23
} // property
person.age  // property

Accessing Object Properties

Object properties can be accessed in multiple ways.

  2. person["name"]
  3. const x = "name"; person[x]

Object Methods

An Object property is an Object method containing function definition. example:

const person = {
    name: 'Jon',
    age: 23,
    sayHi() {
        console.log("Hi, " +;

person.sayHi  // method

Accessing Methods

Similar to accessing object properties, methods can be accessed in multiple ways.

  1. person.sayHi()
  2. person["sayHi"]()
  3. const x = "sayHi"; person[x]()

Object Creation

Objects can be created in multiple ways. Following are the ways explained in detail.

Object Literal

Most simplest list of key: value pair inside curly braces {}

const person = {
    name: 'Jon'

Using new Keyword

If Object() is invoked with a new keyword, it will return an object.

const person = new Object(); = 'jon';
person.sayHi = function sayHi() {
    console.log("Hi, " +;

Using Constructor

To create constructor is nothing but a function invoked with new keyword.

function Person (name) { = name;

Person.prototype.sayHi = function sayHi() {
    console.log("Hi, " +;

const person = new Person('Jon');  // prop
person.sayHi // method

The first two ways of defining objects does exactly the same thing. It’s better to use object literals to create objects in terms of performence, readablity and execution speed.

Object Mutablity

JavaScript objects are mutable by default. Meaning, they can be easily modified after they are defined.

When new variable, the new variable would point to the location of old object instead of copying it. example:

const person = { name: 'Jon', age: 23 };
const person2 = person;  // person === person2

Looping in Object