View difference between Paste ID: d3Sp3pNR and NSf5cxX8

 function solve() {
     class Article {
         constructor(title, content) {
             this.title = title;
             this.content = content;
         }
 
         toString() {
             return `Title: ${this.title}\nContent: ${this.content}`;
         }
     }
 
     class ShortReports extends Article {
         constructor(title, content, originalResearch) {
             if (content.length >= 150) {
                 throw new Error('Short reports content should be less then 150 symbols.');
             }
 
             if (!originalResearch.hasOwnProperty('title') || !originalResearch.hasOwnProperty('author')) {
                 throw new Error('The original research should have author and title.');
             }
             super(title,content);
             this.comments = [];
             this.originalResearch = originalResearch;
         }
 
         addComment(comment) {
             this.comments.push(comment);
             return 'The comment is added.';
         }
 
         toString() {
             let output = super.toString();
             output += `\nOriginal Research: ${this.originalResearch.title} by ${this.originalResearch.author}`;
 
             if (this.comments.length > 0) {
                 output += '\nComments:\n'
                 output += this.comments.join('\n');
             }
 
             return output;
         }
     }
 
     class BookReview extends Article {
         constructor(title, content, book) {
             super(title,content);
             this.book = book;
             this.clients = [];
         }
 
         addClient(clientName, orderDescription) {
            let hasClient =  this.clients.find(client => client.name === clientName
                                             && client.description === orderDescription);
 
             if (hasClient) {
                 throw new Error('This client has already ordered this review.');
             }
 
             this.clients.push({name:clientName,description:orderDescription});
             return `${clientName} has ordered a review for ${orderDescription}`;
         }
 
         toString() {
             let output = super.toString() +'\n';
             output += `Book: ${this.book.name}`;
             if (this.clients.length > 0) {
                 output += '\nOrders:\n';
                 output += this.clients.map(client => `${client.name} - ${client.description}`).join('\n');
             }
 
             return output;
         }
     }
 
     return {Article, ShortReports, BookReview};
 }
 
 let classes = solve();
 let book = new classes.BookReview("The Great Gatsby is so much more than a love story", "The Great Gatsby is in many ways similar to Romeo and Juliet, yet I believe that it is so much more than just a love story. It is also a reflection on the hollowness of a life of leisure. ...", { name: "The Great Gatsby", author: "F Scott Fitzgerald" });
 console.log(book.addClient("The Guardian", "100 symbols"));
 console.log(book.addClient("Goodreads", "30 symbols"));
 console.log(book.toString());