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Javascript framework: Knockout, backbone, ember…

I'm currently on a web application project written in javascript with node.js and Express server-side and it's time to consider the client-side of this application. The two questions are:
Should I consider using a framework or can I write it without such a tool?
And if not, which framework?
I've chosen three of these: backbone, knockout and Ember. I read all the questions I found about them but I'm still hesitating. The points to consider are:
It is good to mix html with javascript like knockout does?
Will my application be easily maintainable?
Will the framework continue and not diappear tomorrow, leaving me in a very uncomfortable situation?
EDIT: And what do you think about JavaScriptMVC?

As #Christian Varga has said in the comments, it depends. However, I would make the following observations:
It is good to mix html with javascript like knockout does?
With knockout you are not forced to mix javascript into the html. See Unobstrusive Event Handling.
Will my application be easily maintainable?
In my experience with knockout , if the application gets especially large the pages do get complicated. However, if you are going for a SPA style page then the code will always get fairly involved. I haven't worked with Ember or Backbone but certainly Backbone does have a reputation for being be good for larger applications.
Will the framework continue and not diappear tomorrow, leaving me in a
very uncomfortable situation?
I think you have picked your three frameworks to consider wisely. Knockout and Backbone both have fairly wide adoption. Knockout is to be shipped with MVC4 which gives you some confidence behind its future. Ember is newer but there seems to be a lot of excitement behind it. There is a good discussion of Ember with various references to knockout and backbone here
Hope this helps you evaluate what will be best for your project.

All those are good frameworks. You can choose anyone and you won't make a huge mistake. Of course, you might like one most than others, but that's a matter of taste. All those frameworks will make your app easy mantainable.
Now, I want to add something more. You asked "Should I consider using a framework"? You can build your own stuff, that's something cool. I'd just recomend to keep in mind good organization of your project. In my short experience, Js is a mess. And these FWs help you to keep your code clean and organized.
1 more thing to add to organization: You should consider some AMD tool, like Require.js

If you're thinking of building an application with scalability and maintainability in mind you might want to consider a reference architecture such as Boilerplatejs.
BoilerplateJS incorporates best practices to be used when building a large scale application. Furthermore it ships with libraries such as knockoutjs and also utilities that would help structure and organize your code.

Javascript: How to make sense of all the frameworks and design philosophies?

I have been a user of jQuery (and some of its minor plugins) for a while. The Javascript code I've developed over the years could be described best as... messy. It used a ton of global variables and functions here and there, didn't use standard ways of organizing the code, nor any design patterns whatsoever.
I am currently building the new version of a website, and I have completed doing the backend with PEAR::MDB2 and Smarty templates. The rest is just homebrew PHP with some classes.
Now I am at the point where I'll add the Javascript layer on top of the website to improve the user-friendliness of some features. (while making sure everything degrades gracefully) I want to write better, cleaner, more organized Javascript than I used to, so I did a little research. I read Stefanov's Object-Oriented Javascript to have a better grasp on some concepts I knew only loosely about (prototypes, constructors, etc.) as well. Now I'm stuck at a point where I wonder which Javascript frameworks I should use, and how to organize it all.
After conducting my research, I understood Cappuccino & Objective-J, and Sproutcore were not what I was looking for. To quote Cappucino's about page:
Cappuccino is not designed for building web sites, or making existing sites more "dynamic". We think these goals are too far removed from those of application development to be served well by a single framework. Projects like Prototype and jQuery are excellent at those tasks
So there's that. Then I found out about Coffee Script, which is more of a one-to-one "compiler" and wouldn't help me with the actual organization of my code.
I also stumbled on some articles that give guidelines:
Using Inheritance Patterns to Organize Large jQuery Applications
A JavaScript Module Pattern
I also found out about Backbone.js, Shoestring, JavaScriptMVC, Google Loader, jQuery Tools, jQuery UI. I don't really know what to do of all this... The things I know:
I don't want to invest too much time in learning something too complex, I want to keep things simple and flexible as much as possible (that is why I don't use Symfony on the backend, for example), yet clean and organized.
I want to use jQuery, the question is, what should I use with it? (that is compatible too)
Right now, I'd use jQuery and jQuery Tools and "organize" all that in a simple namespace/object literal with simple properties and methods and also, since the site is localized, I just plan on using the simple vsprintf (as I do on the backend) with key:value pairs loaded from an object literal provided by the backend. JavaScriptMVC seems interesting, but I fear it would bring way too much complexity for a project that is fairly small sized. That is where I need your advice! Thank you very much in advance.

Ok, my attempt at an answer:
There is no 'best' to way to do it. You now know what's there and I think you might have a preference for yourself for what you want. In that case, pick a framework and learn it inside-out. (sorry to burst your bubble, but each framework has a learning curve, some steep, some very easy, but in the end to use it well you have to invest in it. Just do it, you won't be sorry).
You of course have an preference for clean code, so you might take some considerations into account. You also say you have a preference for jQuery, which is fine, but there are some limitations (as also pointed out in the link provided by eskimoblood).
There are some nice lectures / and tutorials with advice on how to structure your code in jQuery:
How to manage large jquery apps
On Large jQuery apps
Essential Javascript and jQuery patterns (free ebook)
Some style guides:
Jquery core UI Styleguide
Google Closure Javascript Style Guide
Tools for checking your code
JSLint
JSHint (a more forgiving/practical fork)
Closure Linter (haven't tried it yet, but intend to)
Standard works (javascript)
Everything by Douglas Crockford
Quirksmode
There might be more.. perhaps more people can contribute, but I also think that you've almost reached the end of what you can learn before getting your hands dirty. Many of these guides are written in a very generic way, but the interesting thing is that javascript is called upon in many specific situations. It might be useful to just post some of the code that you regard as "messy" and we can help you figure out how to do it better. Good luck!

You should watch the video and read the links in this article and then you should ask yourself again if jquery is the right tool. Maybe you will use dojo, that is much better for larger projects or you take a look at backbone and where you can stay with jquery. After all both of them are more "javascriptish" then something like sproutcore, cappuciono or even GWT. And also much easier to understand when you come from jquery.

One framework that is to consider is definitely ReactJS from Facebook. This framework is pretty slick in many ways.
First thing you have to know is that it is a view framework. It can be used server-side to do the pre-rendering of pages, but it really shines on client side. Since it's a view framework, it can be used with backbone or any other "back-front"-end framework.
One of the main point of React is its rapidity. It keeps a virtual DOM in memory and virtualize all the webpages events. So the virtuals event are used to keep events browser agnostics.
The virtual DOM kind of make programming a dynamic site as if you were programming an old static website. You can just shoot the whole HTML to render to the view engine (as if you were "re-rendering" the whole page) and it will manage the DOM operations. It does a diff between the new virtual DOM and the current virtual DOM and only inserts nodes that needs to be inserted. This way you reduce the number of DOM ops and thus increase your render speed by a lot.
A good place to start is this tutorial which shows how to use "Flux" (the web flow designed by Facebook for its site) in order to realize a Todo application!

Wrap jQuery, dojo with custom library?

Coming from Java, I'm wondering if a Java best practice applies to JavaScript.
In Java, there's a separation of interface and implementation, and mixing them up is considered a bad practice. By the same token, it is recommended to hide implementation details of your library from end developers.
For example, log4J is one of the most popular logging libraries out there but it is recommended to write code to the slf4j library or the Commons Logging library that "wraps" log4j. This way, if you choose to switch to another logging framework such as logback, you can do so without changing your code. Another reason is that you, as a user of a logging library, how logging is done is none of your concern, as long as you know what logging does.
So back to JavaScript, most non-trivial web applications have their own custom JavaScript libraries, many of which use open source libraries such as jQuery and dojo. If a custom library depends on, say jQuery, not as an extension, but as implementation, do you see the need to add another layer that wraps jQuery and makes it transparent to the rest of JavaScript code?
For example, if you have the foo library that contains all your custom, front-end logic, you'd introduce the bar library that just wraps jQuery. This way, your foo library would use the bar library for jQuery functions, but it is totally oblivious to jQuery. In theory, you could switch to other libraries such as dojo and google web toolkit without having a big impact on the foo library.
Do you see any practical value in this? Overkill?

Although it makes sense from a theoretical standpoint, in practice I'd say it's overkill. If nothing else for these two reasons:
Anything that adds to the size of
the request (or adds more requests)
is bad - in web world, less is more.
If you're using say jQuery, the
chances of you switching to
something like Mootools is (imho) slim to none. From what I've seen, the top libraries each aim to solve different problems (at least in the case of Mootools and jQuery - see this great doc for more info on that). I'd assume that you'd incur a tremendous amount of headache if you were to try to implement a middleware library that could easily switch between the two.

In my experience and being a Java developer myself, sometimes we tend to take the whole "abstraction" layer pattern too far, I've seen implementations where someone decided to completely abstract a certain framework just for the sake of "flexibility" but it ends up making things more complicated and creating more code to maintain.
Bottom line is you should look at it on a case by case basis, for example you wouldn't try to create an abstraction layer on top of struts, or on top of JPA, just in case you then go to a different framework (which I've rarely seen done).
My suggestion is, regardless of the framework you are using, create objects and components that use the framework internally, they should model your problem and be able to interact between them without the need of any specific framework.
Hope this helps.

There are a lot of good answers here, but one thing I don't see mentioned is feature sets. If you try to write a library to wrap the functionality provided by, say, jQuery, but you want to be able to easily swap out for something like prototype, you have a problem. The jQuery library doesn't provide all the features prototype provides, and prototype doesn't provide all the features jQuery provides. On top of that, they both provide their features in radically different ways (prototype extends base objects -- that's damn near impossible to wrap).
In the end, if you tried to wrap these libraries in some code that adds 'abstraction' to try to make them more flexible, you're going to lose 80% of what the frameworks provided. You'll lose the fancy interfaces they provide (jQuery provides an awesome $('selector') function, prototype extends base objects), and you'll also have to decide if you want to leave out features. If a given feature is not provided by both frameworks, you have to either ditch it or reimplement it for the other framework. This is a big can of worms.
The whole problem stems from the fact that Java is a very inflexible language. A library provides functionality, and that's it. In JavaScript, the language itself is insanely flexible, and lets you do lots of crazy things (like writing a library, and assigning it to the $ variable). The ability to do crazy things lets developers of javascript libraries provide some really creative functionality, but it means you can't just find commonalities in libraries and write an abstraction. I think writing javascript well requires a significant change in perspective for a Java developer.

Someone wise once said "premature optimization is the root of all evil." I believe that applies in this case.
As others have expressed, you don't want to abstract for the sake of flexibility until you have an actual need for the abstraction. Otherwise you end up doing more work than necessary, and introducing unnecessary complexity before it is required. This costs money and actually makes your code more brittle.
Also, if your code is well organized and well tested, you should not be afraid of major changes. Code is always changing, and trying to anticipate and optimize for a change that may or may not come will almost always get you in more trouble than it saves you.
Acknowledgement: I should give credit to Agile programming and my practice and readings on the topic. What I've said comes directly from my understanding of Agile, and I've found it to be an extremely good razor to cut out the extra fat of my work and get lots done. Also none of what I've said is actually JavaScript specific... I'd apply those principles in any language.

There are good arguments calling this development practice - wrapping in order to switch later - into question in any language.
A good quote by Oren Eini, from his writeup on wrapping ORMs:
Trying to encapsulate to make things
easier to work with, great. Trying to
encapsulate so that you can switch
OR/Ms? Won’t work, will be costly and
painful.

This is definitely something that is done in enterprise environments.
Take for example a company that has their own custom javascript framework that is used on all of their projects. Each of the projects decide to use their own framework (jQuery, Dojo, Prototype) to add functionality to the underlying modules of the company framework. Employees that move between projects can now easily do so because their API with working the project's codebase is still the same, even though the underlying implementation could be different for each project. Abstraction is helpful in these situations.

It is overkill. Javascript is not Java and is not in any way related to Java. It is a completely different language that got J-a-v-a in the name for marketing reasons.
If you are concerned with availability of add-on libraries, then choose a framework with a large ecosystem. In an enterprise environment you will be further ahead by standardising on a vanilla off-the-shelf uncustomised web framework that you can upgrade every year or so tracking the rest of the world. And then supplement that with a SMALL in-house add-on library which you will, of course, have to maintain yourself, not to mention training any new programmers that you hire.
Since you are talking about Javascript in the client (web browser) it is more important that you limit the complexity of the things that people do with it. Don't build huge amounts of client side code, and don't make stuff that is so brittle that another programmer can't maintain it. A web framework helps you both keep the linecount down, and keep your own code reasonably simple.
It is not a question of Javascript best practice, because that would be different for server-side JS such as Rhino or node.js.

Adapter pattern is not a common solution in this case. The only example I know to use this pattern is extjs. Javascript projects are usually too small and they aren't worth the effort you would make by creating such an abstraction layer.
The common solution for this problem is that you try to use multiple frameworks together for example with jquery.noConflict.

I've done this before, and can talk a bit about the experience of writing a library/toolkit wrapper.
The plan was to move from Prototype to some other library. Dojo was the first choice, but at the time I wasn't sure whether that's the library to move everything to (and by everything I mean ~5MB of Prototype-happy JS). So coming from a world of clean interfaces, I was set to write one around Prototype and Dojo; an awesome interface that would make switching out from dojo a breeze, if that was in fact necessary.
That was a mistake that cost a lot of time and effort for a few reasons. The first one is that although two libraries can provide the same functionality, (a) their API will almost always be different, and most importantly (b) the way you program with one library will be different.
To demonstrate, let's take something as common as adding a class-name:
// Prototype
$("target").addClassName('highlighted');
// Dojo
dojo.addClass("target", "highlighted");
// jQuery
$("target").addClass("highlighted");
// MooTools
$('target').set('class', 'highlighted');
Pretty straight-forward so far. Let's complicate it a bit:
// Prototype
Element.addClassName('target', 'highlighted selected');
// Dojo
dojo.addClass("target", ["highlighted", "selected"]);
// jQuery
$("target").addClass(function() {
return 'highlighted selected';
});
// MooTools
$("target").set({
"class": "highlighted selected"
});
Now after choosing an interface for your version of the addClass you have two options: (1) code to the lowest common denominator, or (2) implement all of the non-intersecting features of the libraries.
If you go with the 1st -- you'll loose the "personality" / best qualities of each of the library. If you go with #2 -- your addClass' code will be at 4 times larger than the ones provided by any of the libraries, since for example when Dojo is included, you'll have to write the code for the function as the first param (jQuery) and the Object as the first param (MooTools).
Therefore, although it is theoretically possible, it isn't practical, but is a very nice way to understand the intricacies of the libraries out there.

Ideas for a comprehensive Javascript assignment

I am likely to be part of the teaching team for the web programming course at my University next semester and I was wondering what kind of Javascript assignment to hand out to the students. The course is not an introductory one from a programming perspective.
It is assumed that the students are familiar with OOP, data structures and algorithms, functional programming concepts and working knowledge of networking protocols (HTTP included). This is the first course in which they come in contact with JavaScript
I was thinking to give out something framework-specific (using jQuery perhaps) that involves DOM traversal, some animations and AJAX. The three questions I have in mind are:
should they use a framework or should I have them write vanilla JavaScript?
should I focus more on the functional programming part and on the prototypal inheritance part (more on the language than on working with the DOM)?
how do I automate testing for this? It's better if they have a clear idea on how they will be evaluated. Also, automated testing ensures objectivity and saves me time :).
Outcome
I made them do Tic Tac Toe as a jQuery plugin and the results were mostly satisfactory (70% of the students submitted, generally the submissions were ok).
To prevent copying code from the net, I thought out an API which they had to implement. At least, they'd have to understand the code they found on the net before copy&pasting it into the methods :).
I used QUnit for automated testing, but I also tested each assignment manually because this was the first JavaScript assignment they'd had and I wanted to give relevant feedback.
Thank you all for your ideas, they all helped a lot.
Cheers,
Alex

I think its useful for the students to know fundamentals about the language before working with frameworks. They need to know about JS Scopes, closures, prototypes, the memory model, and everything that makes JS unique.
After that, introduce them to frameworks and the DOM. They'll appreciate them much more since they'll be able to understand the implementation.
As for testing, automated testing might be easy if you have them generate a DOM that you can walk and validate. Mozilla might be able to help you out, esp with JSUnit. You can find info here

I always like the idea of making games to learn new programming concepts. You get a well-defined problem domain that's as simple or complex as you need it, and it's usually more interesting and fun to implement than other problems.
When I wanted to learn Ajax programming I used jQuery and Java server-side to implement the game of chess. It was a fun project, but pretty complicated (at least for me, but I'm primarily a server side programmer). I think something like Tic-Tac-Toe would be substantially simpler, and might be a good idea for a project assignment.
As for the 3 questions:
If this is the only JavaScript assignment, then I'd probably use vanilla instead of jQuery. But if they have a chance to do some assignments before this, I'd consider jQuery, because it just makes JavaScript so much less annoying, and it's also good to know jQuery for future employment possibilities.
I'd place an equal emphasis on both the language and the DOM, because the primary purpose of the language IS to work on the DOM, and the DOM does take some getting used to.
I think Selenium might work for the testing you're trying to do. JsUnit could also be used for unit testing the individual methods.

Start off with vanilla JavaScript to learn the basics. You don't want to create a group that relies on any particular framework that wouldn't know how to do things without it.

I would most definitely have them write vanilla JavaScript. It will encourage all students to better understand the abstractions that frameworks/libraries provide in particular environments i.e. for the most part, in the browser working with the DOM.
I highly recommend having a good text for the course. Object Oriented JavaScript by Stoyan Stefanov is in my mind a great text for learning the language, including some of the topics that many people have difficulty with (prototypes, objects, closures, inheritance, etc). I've read numerous JavaScript books and feel that this particular text best balances the core of the language and it's application in the modern client-side development realm.
You may then want to look at dissecting certain pieces of the source of a particular JavaScript library to gain insight into patterns and practices used in a real-world scenario.

I would have them write vanilla javascript AND also learn how to use jQuery. jQuery is javascript after all, and they need a working knowledge of the language anyway. They'll also need to become SWAT (skills with advanced tools), and I believe anyone not using one of the JS frameworks (or at least their own!) in today's environment is at a serious disadvantage.
See answer 1. I'd teach them about prototypal inheritance in vanilla JS, and about DOM manipulation in jQuery.
Automated testing could be achieved in several ways. 1: produce the correct output given some sample code to start with for the parts that deal with learning JS. 2: for the parts that deal with jQuery, you could provide a reference image for how you expect the result to look, provide an original document, and have them recreate the reference image using jQuery manipulation... sort of like the ACID tests http://acid3.acidtests.org/

Should they use a framework or should I have them write vanilla JavaScript?
To me, it is overwhelmingly import that people new to the language start with the language proper, not modified versions or advanced/fancy libraries that do a lot of the work for you. Besides, if you're starting off not working with the DOM, then you're not getting much benefit from using almost any library, as the bulk of most JavaScript libraries has to do with handling the DOM. Also, it's easier to spot "bad" or ill-performant code when teaching and learning in a "vanilla" environment since you don't have libraries abstracting away the nitty-gritty.
Should I focus more on the functional programming part and on the prototypal inheritance part (more on the language than on working with the DOM)?
Yes! On one hand, the DOM is not not that big of a deal; yet it is also the core of what JavaScript is used to interact with. For starters, I suggest that if you're going to be using a browser environment, you should initially avoid the DOM by using Firebug's console.* methods for output so that you can focus on the "functional programming part and on the prototypal inheritance" and other core concepts. After these core concepts have been covered, then start introducing the DOM. It's best to introduce the DOM later as time will need to be dedicated to cross-browser compatibility, which will only confuse the subject if you are trying to teach the core concepts in tandem.
How do I automate testing for this? It's better if they have a clear idea on how they will be evaluated. Also, automated testing ensures objectivity and saves me time :).
Before (and after) the DOM is introduced, you could use something like JSUnit. Also, see this question: Automated Unit Testing with JavaScript. Once you introduce the DOM, you may want to have the students generate a document that you can walk and validate as SB suggested.

Server side Javascript best practices?

We have a CMS built on Java and it has Mozilla Rhino for the server side JS. At the moment the JS code base is small but growing. Before it is too late and code has become a horrible mess I want to introduce some best practices and coding style.
Obviously the name space control is pretty important. But how about other best practices - especially for Java programmers?

Here's some tips from the front lines:
Like Java, use docblocks in Doxygen/JsDoc style for functions
Unit test. Personally like JsTestDriver, as it can be executed automatically from CI server too.
Use JSLint. It will nitpick about bad code
Consider using Google Closure Compiler. It will nitpick about code like JSLint, but it can be helpful for spotting poor doc blocks etc.
Make sure everyone on your team understands how closures work. Otherwise it'll lead to headaches
As you mention, namespaces are important especially if you want your code to work nice with other JS libraries (var myns = myns || {};)
Personally I find using a library which provides OOP helpers like classes etc. helpful. You could use prototypal inheritance but it's often a bit trickier that way.

As Douglas Crockford likes to say, JavaScript is the worlds most misunderstood programming language. Though many people don't know it, there is a right way to code in JavaScript. I have no doubt that if you let Java developers start coding before understanding how to write good JavaScript you will run into serious trouble.
The first thing to do would be to make sure everyone has read Mozilla's excellent article, A re-introduction to JavaScript (https://developer.mozilla.org/en-US/docs/Web/JavaScript/A_re-introduction_to_JavaScript). One of the biggest problems with JavaScript is that there are many ways to do most common tasks, and this article should get people on the same page. Another essential reference is Douglas Crockford's work, including JavaScript: The Good Parts.
One other thing that gets a lot of Java/C++ programmers is that JavaScript uses function scope NOT block scope. This can cause some very tricky problems. There's a great article about this issue at A List Apart called Binding in JavaScript.
To summarize the major issues talked about in the above resources, the most crucial differences to learn are
how to write object oriented code using prototypal inheritance (vs.class based inheritance)
how to use closures and lambdas
how to utilize the power of dynamic objects
how to write function-scoped code

Since you have a JS engine in Java, make it a habit to write unit tests for your JS code. Select a coding style and apply it vigorously. If possible, use tools to check that the code submits to the coding style.