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why do we need backbone js or any JS MVC framework?

Why do we need to use a JS MVC framework(backbone) if we are already using a backend MVC framework(e.g Django or ROR). I can't understand the concept of two MVC frameworks and how they fit together. I thought all front-end related files or logic(html, css, js) come under the views component of the back-end framework. Can someone explain this in simpler terms?

Backbone lies in the client [browser], in order to have fast interaction and experience.
This way you can take advantage of real-time communication via websockets, or LocalStorage for example.
Using a client MVC [MVVM better, in Backbone's case] implies that you just supply a RESTful set of resource from the server [which you can reuse in many other context], and not a full HTML generation stack.
Said that, client side MVC is closer to desktop/mobile UI-oriented MVC implementations [see Cocoa / iOS] than to web-oriented MVC [Symfony, Django, RoR...].

It's mostly because of scalability, every MV* frameworks allows You to make modular code. To give users high experience by using websites, JS code and some fireworks are necessary. JavaScript gives also posibility to relieve backend side from unnecessary computations and because of these simple facts and the scale of currently made websites (huge amount of modules on backend and on frontend side), such MV* JavaScripts frameworks are made and becomes more and more popular.

You may want to look at this post Why use MVVM?
I have been using MVVM and have found it very useful for the front end. Rendering is much quicker and smoother and view-model binding is done on the client-side.

It seems like one of the reasons these JavaScript MVC frameworks started popping was in an effort to to bring some structure to client side JavaScript code. JavaScript has been used more and more in web apps in recent years because it enhances the client side experience so much but when you keep adding more and more, it can quickly become a big cobbled mess of spaghetti code. If you've ever inherited a web app that has tons of JavaScript, you know it can take a loooong time to sort through all the callbacks, functions, DOM manipulation, etc. that is going on just to to grasp how to app works and is tied together. It can be really messy. These JavaScript MVC frameworks help organize and bring structure too all this code so it doesn't get out of control.

How is AngularJS different from jQuery

I only know one js library and that is jQuery.
But my other coders in the group are changing AngularJS as their default library in new project.
I don't know anything about it. How is it different from jQuery?
I already have a set of functions done for similar tasks in jQuery. Can I still use jQuery stuff with AngularJS?

While Angular 1 was a framework, Angular 2 is a platform. (ref)
To developers, Angular2 provides some features beyond showing data on screen. For example, using angular2 cli tool can help you "pre-compile" your code and generate necessary javascript code (tree-shaking) to shrink the download size down to 35Kish.
Angular2 emulated Shadow DOM. (ref)
This opens a door for server rendering that can address SEO issue and work with Nativescript etc that don't work on browsers.
The official document site
Day one keynote from ng-conf 2016
Resource links
Original:
Basically, jQuery is a great tool for you to manipulate and control DOM elements.
If you only focus on DOM elements and no Data CRUD, like building a website not web application, jQuery is the one of the top tools. (You can use AngularJS for this purpose as well.)
AngularJS is a framework. It has following features
Two way data binding
MVW pattern (MVC-ish)
Template
Custom-directive (reusable components, custom markup)
REST-friendly
Deep Linking (set up a link for any dynamic page)
Form Validation
Server Communication
Localization
Dependency injection
Full testing environment (both unit, e2e)
check this presentation and this great introduction
Don't forget to read the official developer guide
Or learn it from these awesome video tutorials
If you want to watch more tutorial video, check out this post, Collection of best 60+ AngularJS tutorials.
You can use jQuery with AngularJS without any issue.
In fact, AngularJS uses jQuery lite in it, which is a great tool.
From FAQ
Does Angular use the jQuery library?
Yes, Angular can use jQuery if it's present in your app when the
application is being bootstrapped. If jQuery is not present in your
script path, Angular falls back to its own implementation of the
subset of jQuery that we call jQLite.
However, don't try to use jQuery to modify the DOM in AngularJS controllers, do it in your directives.
Update:
Angular2 is released. Here is a great list of resource for starters

I want to add something regarding AngularJS difference with jQuery from a developer's perspective.
In AngularJS you have to have a very structured view and approach on what you want to accomplish. It is scarcely following a linear fashion to complete a task, but rather, the exchanges between various objects take care of the requests and actions, which, then, is necessary as angular is an MVC-Based framework. It also requires an at least general blueprint of the finalized application, since coding depends much on how you want the interactions to be completed.
jQuery is like a free poetry, you write lines and keep some relations and momentum appropriate for your task to be accomplished.
Though, in Angular JS, you should follow some rules as well as keeping the momentum and relations proper, maybe it is more like classical Spencerian sonnet (a famous classical poet) whose poem is structural and tied to many rules.
Compared against AngularJS, jQuery is more like a collection of codes and functions (which is, as already mentioned, great for DOM manipulation and fast-effect achievement), while AngularJS is a real framework which gives the developer the ability to build an enterprise web-application with a lot of data-binding and exchange within a superbly organized-routing and management.
Furthermore, AngularJS has no dependency on jQuery to complete its task. It has two very superb features which are not found in jQuery in any sense:
1- Angular JS teaches you how to CODE and accomplish a goal, not just accomplish a goal by any means. Worth to mention that AngularJS fully utilizes the core and heart of Javascripts and paves the way for you to incorporate in your app, the techniques such as DI (dependency-injection). To work with angularJS you should (or must) learn more elevated techniques of coding with Javascript.
2- Angular JS is fully independent to handle directives and structure your app; you might then simply claim that jQuery can do the same (independence), but, indeed, AngularJS, as several times mentioned within the above lines, has independence in the most excellent possible structurally MVC-Based way.
A last note is that, there is no war of Names, since it is far disturbing to be biased, or subjective. jQuery's magnitude and greatness has been proved, but their usages and limitations( of any framework or software) are the concerns of the discussion and similar debates around.
Update:
Using AngularJS is decisive as it is expensive in terms of implementation, but founds a strong base for future expansion, transformation and maintenance of the application. AngularJS is for the New World of Web. It is targeted toward building applications which are characterized by their least resource consumption (loading only necessary resources from the server), fast response time and high degree of maintainability and extendability wrapped around a structured system.

AngularJS :
AngularJS is for developing heavy web applications. AngularJS can use jQuery if it’s present in the web-app when the application is being bootstrapped. If it's not present in the script path, then AngularJS falls back to its own implementation of the subset of jQuery.
JQuery :
jQuery is a small, fast, and feature-rich JavaScript library. It makes things like HTML document traversal and manipulation, event handling, animation, and Ajax much simpler. jQuery simplifies a lot of the complicated things from JavaScript, like AJAX calls and DOM manipulation.
Read more details here: angularjs-vs-jquery

I think this is a very good chart describing the differences in short. A quick glance at it shows most of the differences.
One thing I would like to add is that, AngularJS can be made to follow the MVVM design pattern while jQuery does not follow any of the standard Object Oriented patterns.

They work at different levels.
The simplest way to view the difference, from a beginner perspective is that jQuery is essentially an abstract of JavaScript, so the way we design a page for JavaScript is pretty much how we will do it for jQuery. Start with the DOM then build a behavior layer on top of that. Not so with Angular.Js. The process really begins from the ground up, so the end result is the desired view.
With jQuery you do dom-manipulations, with Angular.Js you create whole web-applications.
jQuery was built to abstract away the various browser idiosyncracies, and work with the DOM without having to add IE6 checks and so on. Over time, it developed a nice, robust API which allowed us to do a lot of things, but at its core, it is meant for dealing with the DOM, finding elements, changing UI, and so on. Think of it as working directly with nuts and bolts.
Angular.Js was built as a layer on top of jQuery, to add MVC concepts to front end engineering. Instead of giving you APIs to work with DOM, Angular.Js gives you data-binding, templating, custom components (similar to jQuery UI, but declarative instead of triggering through JS) and a whole lot more. Think of it as working at a higher level, with components that you can hook together, instead of directly at the nuts and bolts level.
Additionally, Angular.Js gives you structures and concepts that apply to various projects, like Controllers, Services, and Directives. jQuery itself can be used in multiple (gazillion) ways to do the same thing. Thankfully, that is way less with Angular.Js, which makes it easier to get into and out of projects. It offers a sane way for multiple people to contribute to the same project, without having to relearn a system from scratch.
A short comparison can be this-
jQuery
Can be easily used by those who have proper knowledge on CSS selectors
It is a library used for DOM Manipulations
Has nothing to do with models
Easily manipulate the contents of a webpage
Apply styles to make UI more attractive
Easy DOM traversal
Effects and animation
Simple to make AJAX calls and
Utilities usability
don't have a two-way binding feature
becomes complex and difficult to maintain when the size of a project increases
Sometimes you have to write more code to achieve the same functionality as in Angular.Js
Angular.Js
It is an MVVM Framework
Used for creating SPA (Single Page Applications)
It has key features like routing, directives, two-way data binding, models, dependency injection, unit tests etc
is modular
Maintainable, when project size increases
is Fast
Two-Way data binding
REST friendly
MVC-based Pattern
Deep Linking
Templating
Build-in form Validation
Dependency Injection
Localization
Full Testing Environment
Server Communication
And much more
Think this helps.
More can be found-
jQuery vs. AngularJS: A Comparison and Migration Walkthrough
"Thinking in AngularJS" if I have a jQuery background?
What are the key differences between jQuery and AngularJS?
jQuery Vs AngularJS – A Good Comparison
What is the difference between jQuery and AngularJS?

Jquery :-
jQuery is a lightweight and feature-rich JavaScript Library that helps web developers
by simplifying the usage of client-side scripting for web applications using JavaScript.
It extensively simplifies using JavaScript on a website and it’s lightweight as well as fast.
So, using jQuery, we can:
easily manipulate the contents of a webpage
apply styles to make UI more attractive
easy DOM traversal
effects and animation
simple to make AJAX calls and
utilities and much more…
AngularJS :-
AngularJS is a product by none other the Search Engine Giant Google and it’s an open source
MVC-based framework(considered to be the best and only next generation framework). AngularJS
is a great tool for building highly rich client-side web applications.
As being a framework, it dictates us to follow some rules and a structured approach. It’s
not just a JavaScript library but a framework that is perfectly designed (framework tools
are designed to work together in a truly interconnected way).
In comparison of features jQuery Vs AngularJS, AngularJS simply offers more features:
Two-Way data binding
REST friendly
MVC-based Pattern
Deep Linking
Template
Form Validation
Dependency Injection
Localization
Full Testing Environment
Server Communication

JavaScript GUI library which is usable from ClojureScript?

On one of my ongoing web development projects, we need to create a page (really a mini-application of its own) which will have an interactive, "Web 2.0" interface, more like a graphical desktop application than a typical web page.
I'm hoping to use a higher-level language which can compile down to JS for the client-side logic, rather than programming directly in JS, and ClojureScript is my first choice.
I'm looking for a JS GUI library which can be used from within ClojureScript, and which supports a style of programming similar to "desktop" GUI libraries like Swing, QT, wxWidgets, and so on. It should allow me to create popup <div> "windows", put widgets such as buttons/labels/etc. in them, attach event handlers to the widgets, and so on. Do you know of one which would work?

Clojurescript is still young - I don't think there are mature frameworks of that caliber (yet?). Having said that, I'm building a UI using the following components:
Twitter Bootstrap + JQuery for visuals and UI elements
Chas Emerick's Friend for server-side authentication
Compojure + Ring + Jetty for the server
Crate (Clojurescript Hiccup) for html/dom generating
Jayq for JQuery wrapping
Fetch and/or Shoreleave's remotes for client-server RPC
Shoreleave's pubsub mechanism or Clojure's add-watch for data binding
A good feature of Clojure and Clojurescript are that they favour simple functions on generic data structures. That's why you tend to see several smaller libraries that do one specific job, but work really well together, as opposed to giant monolithic frameworks with an object model that requires you to adopt one way of thinking completely.

You should consider Google Closure Library. It has all features you ask and is definitely usable from ClojuresScript, I've played around with it. See http://closure-library.googlecode.com/svn-history/r1430/docs/index.html

I think ExtJS would fit the best in your case, even though this is pure JS. This is the most advanced web GUI library at the moment and it makes possible to create web applications the way similar the one using the desktop languages and IDEs. Just check out their demos. I don't think there will be something similar for the ClojureScript in the foreseen future.

What kind of architecture should I learn to make good JavaScript based software?

I know Model-View-Controller well, have known about it for years and used it in terms of server-side development with languages like PHP.
However, I am now working with JavaScript and building a big application with it utilizing SVG, Canvas among other great features modern browsers support. The project is big, so, the architecture behind it must not be fragile.
JavaScript and MVC do not get on like a house on fire, because JavaScript is event-driven by nature. So, are there any architectures or anything else I should definitely learn, understand and implement?
The software will have to deal with data. It already utilizes local storage and web SQL database. I need a Models, right? There is an UI, so I have Views? However, do I have Controllers? What about events? How do I structure everything?
Architecture, architecture, architecture -- that's what I'm interested in. I'm fine with the language of my choice.

First, I'm the author of JavaScriptMVC, so I'm extremely biased in a whole variety of ways. First, there are 6ish things you will ever do in a JS application:
Load Scripts
Respond to user events
Update the DOM
Request data from the server
Convert that data into something useful for JavaScript
Organize your front-end business logic
Your choice of architecture might depend on what tools you want / need.
For general architecture, I do think it's important to separate concerns.
I strongly encourage you to find some way of doing dependency management, and client side templates. They will make your life a lot easier.
JavaScriptMVC uses a tiered MVC approach that's based heavily around custom UI events and OpenAjax events.
I build my low-level widgets with $.Controller in a similar way to how you would build jQuery widgets. The big difference is that the widgets produce a non-ui event that top level controllers can listen to. For example, a tabs widget might produce a "tab.activate" event like:
$('.tab').trigger('tab.activated')
Then, my higher order controller might listen to tab.activated events, and a the model to update the tab content like:
".flickr tab.activated" : function(tabEl, ev){
Flickr.findAll({type : "rainbows"}, function(images){
tabEl.html("//path/to/view", images );
}
}
Flickr.findAll essentially does a query for flickr messages, then calls back with a list of images. Wrapping the service/ajax functionality with models makes them a lot more reusable.
You'll notice that in the callback I update the html of the tab element with the rendered content from a view. This probably isn't the 'best' way of doing it, but I wanted a quick example. Better would be passing the tabs controller the rendered output, for it to do what it will with it. That way if your tab wants to fade in content someday, it will be able to and your master controller won't have to know about the tab's implementation.
The most important thing is to break down your app into the smallest pieces you can. Have them individually testable (and flexible), and combine the little parts into bigger parts as you work your way up to your application.

Take a look at Ext JS. It has a clean architecture that is well-suited towards highly complex javascript applications.
Data handling and server communication is done via stores. Data rendering is done via grids (with in-cell editors), and forms (with a rich set of form controls), which can both talk to the stores. There's also a set of layout classes to abstract away CSS positioning (border layout, box layout, table layout, form layout, ...).
It is however not MVC in the typical sense. The library encourages a programming style that avoids dealing much with HTML and CSS, letting you live (mostly) in pure JavaScript land. You end up thinking in terms of components and data, instead of individual dom elements and style rules. If you don't like that approach, be warned, you won't like this library.

MVC is still the way to go, in my opinion. If you're looking for a good framework to help you achieve that a little less painfully, I would look at JavaScript MVC, it has models, views, controllers, unit testing, jQuery support, etc.

You should learn the Event Based nature of client-side JavaScript and how it blends with MVC based server-side applications.
You should also learn how to properly program inside of the Prototype based inheritance structure of Javascript.
Both of those things will allow you to write you JavaScript so that it meshes with your server-side application framework and is extensible and re-usable.

One thing i have learned over the years of javascript programming is writing UnObtrusive Javascripting which basically means seperating as much as possible structure(HTML) and style(CSS) from Behaviour(JAVASCRIPT).

Althogh not a raw javascript solution, take a look at CoreMVC, the jQuery architechure of MVC.
CorMVC is a jQuery-powered
Model-View-Controller (MVC) framework
that can aide in the development of
single-page, web-based applications.
CorMVC stands for client-only-required
model-view-controller and is designed
to be lowest possible entry point to
learning about single-page application
architecture. It does not presuppose
any server-side technologies, or a web
server of any kind, and requires no
more than a web browser to get up and
running.

If you want a ready-made reference architecture that combines soem industry leading JS libraries with some good JS design patterns for large scale development, have a look at:
http://boilerplatejs.org/
I'm the main author of it and thought of sharing knowledge we gained after developing few large scale javascript products. It addresses following main concerns:
Solution structuring
Creating complex module hierarchy
Self contained UI components
Event based inter module communication
Routing, History, Bookmarking
Unit Testing
Localization
Document Generation

Architecture of a single-page JavaScript web application?

How should a complex single-page JS web application be structured on the client-side? Specifically I'm curious about how to cleanly structure the application in terms of its model objects, UI components, any controllers, and objects handling server persistence.
MVC seemed like a fit at first. But with UI components nested at various depths (each with their own way of acting on/reacting to model data, and each generating events which they themselves may or may not handle directly), it doesn't seem like MVC can be cleanly applied. (But please correct me if that's not the case.)
--
(This question resulted in two suggestions of using ajax, which is obviously needed for anything other than the most trivial one-page app.)

MVC architecture of PureMVC/JS is the most elegant IMO. I learned a lot from it. I also found Scalable JavaScript Application Architecture by Nicholas Zakas helpful in researching client side architecture options.
Two other tips
I've found view, focus, and input management are areas that need special attention in single page web apps
I also found it helpful to abstract away the JS library, leaving door open to change mind on what you use, or mix & match should the need arise.

Nicholas Zakas's presentation as shared by Dean is a very good place to start with. I was also struggling to answer the same question for a while. After doing couple of large scale Javascript products, thought of sharing the learnings as a reference architecture in case someone needs it. Have a look at:
http://boilerplatejs.org/
It addresses common Javascript development concerns such as:
Solution structuring
Creating complex module hierarchy
Self contained UI components
Event based inter module communication
Routing, History, Bookmarking
Unit Testing
Localization
Document Generation
etc.

The way I build apps:
ExtJS framework, single page app, every component defined in a separate JS file, loaded on-demand
Every component contacts its own dedicated web service (sometimes more than one), fetching data into ExtJS stores or special-purpose data structures
The rendering uses standard ExtJS components, so I can bind stores to grids, load forms from records, ...
Just choose a javascript framework, and follow its best practices. My favorites are ExtJS and GWT, but YMMV.
Do NOT roll your own solution for this. The effort required to duplicate what modern javascript frameworks do is too big. It is always faster to adapt something existing than to build it all from scratch.

Question - What makes an application complex ?
Answer - The use of word 'complex' in the question itself. Hence, a common tendency will be to look out for a complex solution right from the beginning.
Question - What does the word complex means ?
Answer - Anything that is unknown or partially understood. Example : The theory of Gravity even today is COMPLEX to me but not to Sir Isaac Newton who discovered it in 1655.
Question - What tools can I use to deal with complexity ?
Answer - Understanding and simplicity.
Question - But I understand my application . Its still complex ?
Answer - Think twice, because understanding and complexity does not co-exist. If you understand a huge huge application, I am sure you will agree that it is nothing but an integration of small and simple units.
Question - Why all of the above philosophical discussion for a question on
Single Page Application (SAP)?
Answer - Because,
-> SPA is not some kind of core technology that is newly invented for which we need to reinvent the wheel for a lot of things that we are doing in application development.
-> Its a concept driven by the need for better performance, availability, scalability and maintainability of web applications.
-> Its a fairly newly identified design pattern, so an understanding of SPA as a design pattern goes long way in making informed decisions about the architecture of a SPA.
-> At the root level no SPA is complex, because after understanding the needs of an application and the SPA pattern, you will realize that you are still creating an application, pretty much the same way you did before with some modifications and re-arrangements in the development approach.
Question - What about the use of Frameworks ?
Answer - Frameworks are boiler plate code / solution for some commonly identified and generic patterns, hence they can take off x% (variable, based on the application) load from application development but then not a lot should be expected out of them specially for heavy and growing applications. Its always a good case to be in complete control of your application structure and flow but most importantly the code for it. There should be no grey or black areas in the application code.
Question - Can you suggest one of the many approaches to SPA architecture ?
Answer - Think of your own framework based on the nature of your application. Categorize application components. Look for an existing framework that is close to your derived framework, if you find it then use it, if you do not find it then I suggest going ahead with your own. Creating framework is quite an effort upfront but produces better results in long run. Some basic components in my SPA framework will be:
Data Source : Models / Collections of Models
Mark Up for presenting data : Templates
Interaction with the application : Events
State capturing and navigation : Routing
Utilities , widgets and plug-ins : libraries
Let me know if this helped in any way and good luck with your SPA architecture !!

The best thing to do is to look at example uses of other frameworks:
TodoMVC showcases many many SPA frameworks.

You can use javascript MVC framework http://javascriptmvc.com/

The web application that I am currently working on uses JQuery and I would not recommend it for any large single page web application. Most frameworks i.e. Dojo, yahoo, google and others use namespaces in their libraries but JQuery does not and this is a significant drawback.
If your web site is intended to be small then JQuery would be ok but if you intended to build a large site then I would recommend looking at all the Javascript frameworks available and deciding which one most meets your needs.
And I would recommend applying the MVC pattern to your javascript/html and probably most of your object model for the javascript could be done as the json that you actually return from the server through ajax and the javascirpt uses the json to render html.
I would recommend reading the book Ajax in action as it covers most of the stuff you will need to know.

I'm using Samm.js in several one page applications with great success

I would go with jQuery MVC

Check out http://bennadel.com/projects/cormvc-jquery-framework.htm Ben is pretty sharp and if you dig around on his blog he has some nice posts about how CorMVC is put together and why.

Alternative: take a look to ItsNat
Think in JavaScript but code the same in Java in server with the same DOM APIs, in server is way easier to manage your application without custom client/bridges because UI and data are together.

Or have a look at https://github.com/flosse/scaleApp

NikaFramework allows you to create single-page application. Also allows you to write HTML, CSS (SASS), JavaScript into separate files and bundle them into only one output file in the end.

I would recommend to explore Yeoman. It allow you to use existing "best practice" for your new project.
For example:
if you decide to use Angular.js, there is a Yeoman generator, that give you a structure for routing, views, services, etc. Also allow you to Test, minify your code, etc.
If you decide to use Backbone, checkout this generator