JavaScript Objects

An Object is a variable that can hold many variables.

Objects are collections of key-value pairs, where each key (known as property names) has a value.

Objects can describe anything like houses, cars, people, animals, or any other subjects.

Car Object

Car Properties	Car Methods
car.name = Fiat car.model = 500 car.weight = 850kg car.color = white	car.start() car.drive() car.brake() car.stop()

Different cars have the same properties, but the property values can differ from car to car.

Different cars have the same methods, but the methods can be performed at different times.

JavaScript Objects

This code assigns many values (Fiat, 500, white) to an object named car:

Example

const car = {type:"Fiat", model:"500", color:"white"};

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Note:

You should declare objects with the const keyword.

When an object is declared with const, you cannot later reassign it to point to a different variable.

It does not make the object unchangeable. You can still modify its properties and values.

How to Create a JavaScript Object

An object literal is a concise way to create an object.

An object literal is a list of key : value pairs inside curly braces { }:

{firstName:"John", lastName:"Doe", age:50, eyeColor:"blue"}

In object terms, the key : value pairs are the object properties.

Examples

All the examples below, create a JavaScript object with 4 properties.

// Create an Object
const person = {firstName:"John", lastName:"Doe", age:50, eyeColor:"blue"};

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Spaces and line breaks are not important. An object literal can span multiple lines:

// Create an Object
const person = {
firstName: "John",
lastName: "Doe",
age: 50,
eyeColor: "blue"
};

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You can also create an empty object, and add the properties later:

// Create an Object
const person = {};

// Add Properties
person.firstName = "John";
person.lastName = "Doe";
person.age = 50;
person.eyeColor = "blue";

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Using the new Keyword

Example

Create a new JavaScript object using new Object():

// Create an Object
const person = new Object({
  firstName: "John",
  lastName: "Doe",
  age: 50,
  eyeColor: "blue"
});

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Note:

All the examples above do exactly the same.

There is no need to use new Object().

For readability, simplicity and speed, use an object literal instead.

Object Properties

You can access object properties in two ways:

objectName.propertyName

objectName["propertyName"]

Examples

person.lastName;

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person["lastName"];

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JavaScript Object Methods

Object methods are actions that can be performed on objects.

Object methods are function definitions stored as property values:

Property	Property Value
firstName	John
lastName	Doe
age	50
eyeColor	blue
fullName	function() {return this.firstName + " " + this.lastName;}

Example

const person = {
firstName: "John",
lastName : "Doe",
id       : 5566,
fullName : function() {
    return this.firstName + " " + this.lastName;
  }
};

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In the example above, this refers to the person object:

this.firstName means the firstName property of person.

this.lastName means the lastName property of person.

How to Display JavaScript Objects?

Displaying a JavaScript object will output [object Object].

Example

// Create an Object
const person = {
name: "John",
age: 30,
city: "New York"
};

let text = person;

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Displaying Object Properties

The properties of an object can be added in a string:

Example

// Create an Object
const person = {
name: "John",
age: 30,
city: "New York"
};

// Add Properties
let text = person.name + "," + person.age + "," + person.city;

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Object Constructor Functions

Sometimes we need to create many objects of the same type.

To create an object type we use an object constructor function.

It is considered good practice to name constructor functions with an upper-case first letter.

Object Type Person

function Person(first, last, age, eye) {
  this.firstName = first;
  this.lastName = last;
  this.age = age;
  this.eyeColor = eye;
}

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Note:

In the constructor function, this has no value.

The value of this will become the new object when a new object is created.

Now we can use new Person() to create many new Person objects:

Example

const myFather = new Person("John", "Doe", 50, "blue");
const myMother = new Person("Sally", "Rally", 48, "green");
const mySister = new Person("Anna", "Rally", 18, "green");

const mySelf = new Person("Johnny", "Rally", 22, "green");

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