Object-oriented programming with classes

ES2015 also introduced a cleaner way of declaring classes. You learned that we can declare a class named Book in the object-oriented programming section this way:

function Book(title, pages, isbn) { // {1} 
  this.title = title; 
  this.pages = pages; 
  this.isbn = isbn; 
}  
Book.prototype.printTitle = function() { 
  console.log(this.title); 
}; 

With ES2015, we can simplify the syntax and use the following code:

class Book { // {2}
  constructor(title, pages, isbn) { 
    this.title = title; 
    this.pages = pages; 
    this.isbn = isbn; 
  } 
  printIsbn() { 
    console.log(this.isbn); 
  } 
} 

We can simply use the keyword class and declare a class with a constructor function and other functions as well—for example, the printIsbn function. ES2015 classes are syntactical sugar over the prototype-based syntax. The code for the Book class declared in line {1} has the same behavior and output as the code declared in line {2}:

let book = new Book('title', 'pag', 'isbn'); 
console.log(book.title); // outputs the book title 
book.title = 'new title'; // update the value of the book title 
console.log(book.title); // outputs the book title