JavaScript Objects

What are JavaScript Objects?

Objects are variables that can store both values and functions.

Values are stored as key:value pairs called properties.

Functions are stored as key:function() pairs called methods.

Real Life Comparison

In real life, we can describe subjects as objects (a car, a person, a house)

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.

Object Example

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

Example

const car = {

      type: "Fiat",

      model: "500",

      color: "white"

    };

Object Literal

An object literal "literally" describes an object using a concise syntax with zero or more key:value pairs inside curly braces to describe all the object properties:

Example

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

How to Create a JavaScript Object

An object literal is the simplest and most common way to define a JavaScript object.

All the examples below, create the same JavaScript object:

Example 1

// Create an Object

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

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

Example 2

// Create an Object

const person = {

  firstName: "John",

  lastName: "Doe",

  age: 50,

  eyeColor: "blue"

};

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

Example 3

// Create an Object

const person = {};

// Add Properties

person.firstName = "John";

person.lastName = "Doe";

person.age = 50;

person.eyeColor = "blue";

Using the new Keyword

Example 4

// Create an Object

const person = new Object({

  firstName: "John",

  lastName: "Doe",

  age: 50,

  eyeColor: "blue"

});

Object Properties

You can access object properties in two ways:

• Dot notation
• Bracket notation

Dot Notation

objectName.propertyName

Bracket Notation

objectName["propertyName"]

JavaScript Object Methods

Objects can also have methods.

Object methods are actions that can be performed on objects.

Object methods are function definitions stored as property values:

Example

const person = {

    firstName: "John",

    lastName : "Doe",

    age      : 50,

    fullName : function() {

    return this.firstName + " " + this.lastName;
  }

};

Summary

• Objects are containers for Properties and Methods
• Properties are named Values stored as key:value pairs
• Methods are Functions stored as key:function() pairs.

In JavaScript, Objects are King

If you Understand Objects, you Understand JavaScript.

In JavaScript, almost "everything" is an object:

• Objects are objects
• Maths are objects
• Dates are objects
• Arrays are objects
• Maps are objects
• Sets are objects
• RegExp are Objects
• Errors are Objects

All JavaScript values, except primitives, are objects.

JavaScript Primitives

A primitive data type is data type that can only store a single primitive value.

JavaScript defines 7 types of primitive data types: