Edit in JSFiddle

 //binding click functions
 document.getElementById("btn-author").onclick = function() {
   filterAuthor('Dan Brown');
 };
 document.getElementById("btn-subject").onclick = function() {
   filterSubject('Comedy');
 };

 //app object
 var App = {
   Models: {},
   Collections: {}
 };

 //model
 App.Models.Book = Backbone.Model.extend({
   title: "title",
   author: "author",
   subject: "subject",
   printDetails: function() {
     return "<b>title: </b>" + this.get('title') + ", <b>author: </b>" + this.get('author') + ", <b>subject: </b>" + this.get("subject");
   }
 });

 //collection
 App.Collections.Library = Backbone.Collection.extend({
   model: App.Models.Book,
   url: "/connectors",
   filterByAuthor: function(author) { //filtering the models of a collection based on a condition
     //map using usual JS mapping method
     return this.filter(function(d) {
       return d.get('author') === author;
     });
   },
   filterBySubject: function(subject) {
     //map using ECMAscript 6 arrow functions
     return this.filter(d => d.get('subject') === subject);
   }
 });

 //initialize books
 var book1 = new App.Models.Book({
   title: "Digital Fortress",
   author: "Dan Brown",
   subject: "Thriller"
 });
 var book2 = new App.Models.Book({
   title: "The Lost Symbol",
   author: "Dan Brown",
   subject: "Comedy"
 });
 var book3 = new App.Models.Book({
   title: "Love from both sides",
   author: "Nick Spalding",
   subject: "Romance"
 });
 var book4 = new App.Models.Book({
   title: "Oh my venus",
   author: "Shin Min Ah",
   subject: "Comedy"
 });

 //initializ collection - library
 var library = new App.Collections.Library([book1, book2, book3, book4]);

 function filterAuthor(author) {
   var set = library.filterByAuthor(author); //array of books
   var toPrint = "";
   set.map(function(book) { //iterate through the array of books  
     toPrint += book.printDetails() + "<br>"; //generate html string
   });
   document.getElementById("filter-by-author").innerHTML = toPrint;
 }

 function filterSubject(subject) {
   var set = library.filterBySubject(subject); //array of books
   var toPrint = "";
   set.map(function(book) { //iterate through the array of books  
     toPrint += book.printDetails() + "<br>"; //generate html string
   });
   document.getElementById("filter-by-subject").innerHTML = toPrint;
 }

<div class="box">
  <button id="btn-author">Filter by author (Dan Brown)</button>
  <div class='result' id="filter-by-author"></div>
</div>
<div class="box">
  <button id="btn-subject">Filter by subject (Comedy)</button>
  <div class='result' id="filter-by-subject"></div>
</div>

 .box {
   height: auto;
   border: 1px solid black;
   border-radius: 10px;
   padding: 10px;
   margin: 30px;
 }
 
 .result {
   border: 1px solid #c9c9c9;
   border-radius: 10px;
   height: 200px;
   padding: 5px;
   margin: 10px;
 }