Backbone js Interview Questions & Answers (2025)

Backbone.js is a client-side (Model, View, Controller) MVC-based JavaScript framework. It purely is written in Javascript.

Backbone.js gives structure to web applications by providing models with key-value binding and custom events, collections with a rich API of enumerable functions views with declarative event handling, and connects it all to your existing API over a RESTful JSON interface.

Backbone’s Js only hard dependency is Underscore.js ( >= 1.8.3). For RESTful persistence and DOM manipulation with Backbone. View, include jQuery ( >= 1.11.0), and json2.js for older Internet Explorer support. (Mimics of the Underscore and jQuery APIs, such as Lodash and Zepto, will also tend to work, with varying degrees of compatibility.)

The Backbone.js router is used to change the URL fragment or hashes of an application to create bookmarkable and shareable URLs.

In Backbone.js, the collection is used to represent ordered set of models. Any event in model triggers an event in collection directly. For example, you can bind “change” event to be notified in a case when any model in the collection has been modified.

The main native components of BackboneJs are:-

• Model
• View
• Collection
• Router
• Event class object

Backbone events is a module that can be mixed into any object, giving the object the ability to bind and trigger custom named events. Events are not declared before they are bound to any object. Events reflect the state of the model.

The “id” property on a model is automatically assigned based on the “id” set in the model’s attributes hash.

Ideally, this is the ID that you receive from the rest API for the resource that you are querying. On the other hand, “cid” is an ID temporarily assigned to each model and is useful until an actual ID is determined for the object. For example, a model pushed to a collection that has not yet been persisted can be addressed using “cid”, until it is saved in the database and an actual ID is generated for it.

• InitialCopyDirection
• modelSetOptions
• change Triggers
• boundAttribute
• suppressThrows
• converter

ModelBinder class is used to make synchronization process of views and models together.

When a model’s attribute is copied to an HTML element or when an HTML element’s value is copied into a model’s attribute, a function is called, this function is known as a converter in Backbone Js.

Also, Read  Best 25 React js Interview questions

Below image shows the Architecture of Backbone.js

Backbone.sync is a function that is Backbone js call every time it attempts to read or save a model to the server.By default, it uses jQuery.ajax to make a RESTful JSON request and returns a jqXHR

Example Code

Backbone.sync = function(method, model) {
  alert(method + ": " + JSON.stringify(model));
  model.set('id', 1);
};

var author= new Backbone.Model({
  author: "Sharad",
  website: "https://www.onlineinterviewquestions.com"
});

author.save();

author.save({author: "Teddy"});

ModelBinder is a class in Backbone.js to bind backbone model attributes to:

• Read-only html elements such as <span>, <div> etc.
• Html element attributes such as enabled, displayed, style etc.
• Editable form elements such as <input>, <textarea> etc. This type of binding is bidirectional between the HTML elements and the Model’s attributes.

In order to access a models data from a view in backbone.js you have to initialize your Model :

var author= Backbone.Model.extend({
      initialize: function(){
        console.log('intailized');
      },
      defaults:{
          names:['Bob','Sim','Dart']
      }
    })
var person_view = Backbone.View.extend({
    initialize: function() {
        this.model = new author();
    },
    output: function(){
        console.log(this.model.get('names'))
    }
});

In Backbone.js models attributes stored in a hash.

Backbone Router is used for routing client-side applications and connects them to actions and events using URLs. Backbone.Router is used to create a Router with Backbone.

A collection is a set of models which binds events when the model has been modified in the collection. The collection contains a list of models that can be processed in the loop and supports sorting and filtering. When creating a collection, we can define what type of model that collection is going to have along with the instance of properties. Any event triggered on a model, which will also trigger on the collection in the model.

Creating a Model in Backbone Js

Person = Backbone.Model.extend({
initialize: function(){
alert("Welcome to Backbone Js");
}
});

var person = new Person;