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JavaScript Object Introduction

JS Object Introduction

In JavaScript, objects are king. If you understand objects, you understand JavaScript.

JavaScript Objects

In JavaScript, almost "everything" is an object.

Booleans can be objects (if defined with the new keyword)
Numbers can be objects (if defined with the new keyword)
Strings can be objects (if defined with the new keyword)
Dates are always objects
Maths are always objects
Regular expressions are always objects
Arrays are always objects
Functions are always objects
Objects are always objects

Objects are variables too. But objects can contain many values.

The values are written as name:value pairs (name and value separated by a colon). It is a common practice to declare objects with the const keyword.

					 
        
          const user = { name:"John Doe", email:"john@gmail.com" };

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Creating a JavaScript Object

With JavaScript, you can define and create your own objects. There are different ways to create new objects.

Create a single object, using an object literal.
Create a single object, with the keyword new.
Define an object constructor, and then create objects of the constructed type.
Create an object using Object.create().

Using an Object Literal

This is the easiest way to create a JavaScript Object.

Using an object literal, you both define and create an object in one statement.

An object literal is a list of name:value pairs (like age:50) inside curly braces {}.

					 
        
          const user = { name:"John Doe", email:"john@gmail.com" };

          // OR
          const user = {
            name:"John Doe",
            email:"john@gmail.com"
          };

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Using the JavaScript Keyword new

You can create an object using new Object().

					 
        
          const user = new Object();
          user.name = "John Doe";
          user.email = "john@gmail.com";

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There is no need to use new Object(). For readability, simplicity and execution speed, use the object literal method.

					 
        
          const user = {};
          user.name = "John Doe";
          user.email = "john@gmail.com";

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JavaScript Objects are Mutable

Objects are mutable. They are addressed by reference, not by value.

					 
        
          const x = user;  // Will not create a copy of user.

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The object x is not a copy of user. It is user. Both x and user are the same object.

Any changes to x will also change user, because x and user are the same object.

					 
        
          const user = { name:"John Doe", email:"john@gmail.com" };
          const x = user;
          x.email = "john@gmail.com";      // Will change both x.email and user.email

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View JS PDF Ebooks

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JavaScript Object Introduction

JS Object Introduction

JavaScript Objects

Creating a JavaScript Object

Using an Object Literal

Using the JavaScript Keyword new

JavaScript Objects are Mutable

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