Object-oriented programming

JavaScript objects are very simple collections of name-value pairs. There are two ways of creating a simple object in JavaScript. The first way is as follows:

var obj = new Object();

And the second way is as follows:

var obj = {};

We can also create an object entirely as follows:

obj = {
    name: {
        first: 'Gandalf',
        last: 'the Grey'
    },
    address: 'Middle Earth'
};

In object-oriented programming (OOP), an object is an instance of a class. A class defines the characteristics of the object. For our algorithms and data structures, we will create some classes that will represent them. This is how we can declare a class that represents a book:

function Book(title, pages, isbn){
    this.title = title;
    this.pages = pages;
    this.isbn = isbn;
}

To instantiate this class, we can use the following code:

var book = new Book('title', 'pag',  'isbn');

Then, we can access its attributes and update them as follows:

console.log(book.title); //outputs the book title
book.title = 'new title'; //updates the value of the book title
console.log(book.title); //outputs the updated value

A class can also contain functions. We can declare and use a function as the following code demonstrates:

Book.prototype.printTitle = function(){
    console.log(this.title);
};
book.printTitle();

We can declare functions directly inside the class definition as well:

function Book(title, pages, isbn){
    this.title = title;
    this.pages = pages;
    this.isbn = isbn;
    this.printIsbn = function(){
        console.log(this.isbn);
    }
}
book.printIsbn();

Note

In the prototype example, the printTitle function is going to be shared between all instances, and only one copy is going to be created. When we use class-based definition, as in the previous example, each instance will have its own copy of the functions. Using the prototype method saves memory and processing cost in regards to assigning the functions to the instance. However, you can only declare public functions and properties using the prototype method. With a class-based definition, you can declare private functions and properties and the other methods inside the class can also access them. You will notice in the examples of this book that we use a class-based definition (because we want to keep some properties and functions private). But, whenever possible, we should use the prototype method.

Now we have covered all the basic JavaScript concepts that are needed for us to start having some fun with data structures and algorithms!