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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
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!
The previous programmer left the website in pretty unusable state, and I am having difficulty modifying anything. I am new to web design so I don't know whether my skills are a mismatch to this kind of job or is it normal in the real industry to have websites like these
The Home page includes three frames
Each of these frames have their own javascript functions ( between <head>, and also call other common javascript functions (using <script src=..>
Excessive usage of document.all - in fact the elements are referred or accessed by document.all only.
Excessive usage of XSLT and Web Services - Though I know that using Web Services is generally considered a good design choice - is there any other way I can consume these services other than using xslt. For example, the menu is created using the data returned by a web method.
Every <div>, <td> and every other element has an id, and these id's are manipulated by the javascript functions, and then some appropriate web service and the xslt files are loaded based on these..
From the security perspective, he used T-SQL's for xml auto for most of the data that is returned by the web service - is it a good choice from the security standpoint to expose the table names and column names to the end user??
I am a lot confused about the state of the application itself. Should I learn about the intricacies that he has developed and continue working on it, or should I start rewriting everything? What I am perplexed a lot is the lack of alternatives - and whether this is the common way web projects are handled in the real world or was it an exception?
Any suggestions, any pointers are welcome. Thanks
No, it is not acceptable in this industry that people keep writing un-maintainable code.
My advice to you is to go up the chain and convince everyone that this needs to be rewritten. If they question you, find an external consultant with relevant web development skills to review the application (for 1 day).
Keeping this website as-is, because it 'works' is like keeping a working model Ford-T car on today's highways, very dangerous. Security and maintenance costs are likely the most persuading topics to convince anyone against keeping this site 'as-is'.
Next, get yourself trained, it will pay off if you can rewrite this application knowing the basics. Todays technology (asp.net MVC) allows you to implement core business value faster than trying to maintain this unconventionally written app.
Tough spot for an inexperienced developer (or any) to be left in. I think you have a few hard weeks a head of you where you really need to read up on the technologies involved to get a better understanding of them and what is best practice. You will also need to really dig down into the existing code to understand how it all hangs together.
When you done all that you really need to think about your options. Usually re-writing something from scratch (especially if it actually works) is a bad idea. This obviously depend on the size of the project, for a smaller projects with only a couple of thousand lines of code it might be OK. When looking at someone elses code it is also easy to overlook that all that weird shit going on could actually be fixes for valid requirements. Things often start out looking neat, but then the real words comes visiting.
You will need to present the business with time estimates for re-writing to see if that is an option at all, but I'm guessing you will need to accept the way things are and do your best with what you have. Maybe you could gradually improves things.
I would recommend moving the project to MVC3 and rewriting the XSLT portions to function using views and/or partial views with MVC. The Razor model binding syntax is very clean and should be able to quickly cleave out the dirty XSLT code and be left with just the model properties you would need.
I would then have those web services invoked from MVC serverside and for you to deserialize the object results into real objects (or even just use straight XQuery or Json traversing to directly pull stuff out for your model) and bind those to your views.
This could be a rather gargantuan leap for technology at your company though. Some places have aversion to change.
I'd guess this was written 6-7 years ago, and hacked on since then. Every project accumulates a certain amount of bubble gum and duct tape. Sounds like this one's got it bad. I suggest breaking this up into bite size chunks. I assume that the site is actually working right now? So you don't want to break anything, the "business" often thinks "it was working just fine when the last guy was here."
Get a feel for your biggest pain points for maintaining the project, and what you'll get the biggest wins from fixing. a rewrite is great, if you have the time and support. But if it's a complex site, there's a lot to be said for a mature application. Mature in the sense that it fulfills the business needs, not that it's good code.
Also, working on small parts will get you better acquainted with the project and the business needs, so when you start the rewrite you'll have a better perspective.
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
I would like to create a database backed interactive AJAX webapp which has a custom (specific kind of events, editing) calendaring system. This would involve quite a lot of JavaScript and AJAX, and I thought about Google Web Toolkit for the interface and Ruby on Rails for server side.
Is Google Web Toolkit reliable and good? What hidden risks might be if I choose Google Web Toolkit? Can one easily combine it with Ruby on Rails on server side? Or should I try to use directly a JavaScript library like jQuery?
I have no experience in web development except some HTML, but I am an experienced programmer (c++, java, c#), and I would like to use only free tools for this project.
RoR is actually one of the things the GWT is made to work well with, as long as you're using REST properly. It's in the Google Web Toolkit Applications book, and you can see a demo from the book using this kind of idea here. That's not to say that you won't have any problems, but I think the support is definitely out there for it.
There's a neat project for making RoR/GWT easy that you can find here (MIT license). I haven't had a chance to try it out yet, but it looks like a good amount of thought has been put into it. One catch is that it looks like it hasn't been fully tested with 2.1 Rails yet, just 2.0, so you may run into a few (probably minor and fixable) errors.
If you are looking to integrate GWT with non-Java backends such as ROR, PHP etc., you should bear in mind that GWT 1.5 now supports JavaScript Overlay types. This feature lets you write classes that can be mapped over the top of native JavaScript objects to easily provide accessor methods for properties of those objects and other extended functionality.
See this link for more details:
JavaScript Overlay Types
So you could return JSON encoded data from your backend via AJAX calls, parse it into a JavaScript Object and then access the data through your GWT Java code using the overlay classes you've created. Or when you render your page you can render static config data as JavaScript Objects and read it in via this mechanism, rather than having to do an AJAX call to grab the data.
If you know JAVA, and have somewhere you can host it (like a tomcat or glassfish container) I would recommend that much more than using Ruby for the back end. The main reason is that then you can share all of your objects, and use the built in RPC mechanism. I've done this for quite a lot of our projects and it's a huge timesaver, not to mention that the code is less error prone, because you don't convert your java objects to anything and then back again.
I have linked my GWT with Rails before, using the to_json function in Rails and then reading the JSON in GWT. It's all supported, but it is far more annoying than just doing the back end in JAVA.
Of course if you have cheap hosting, then Java containers are pretty much out of the question, in which case I would think Rails would be the next best thing.
GWT is very high quality with a great community. However you do need to know CSS if you want to adjust the look of things (you will) - CSS can do a lot of the layout, just like regular web if you want it to. Libraries like GWT-ext or ExtGWT can help a bit as they have stunning "out of the box" looks but for a price (extra size to your app).
You can code everything in Java using GWT, and you can integrate existing 3rd party javascript libraries with it. It's very good. I've never used RoR much though, so can't say anything about that.
If you're experienced in Java but not in Javascript/CSS, then GWT is going to be a lifesaver (unless you want to learn them, of course). CSS has so many little fiddly details. It is not uncommon to spend half a day fixing a 2 pixel misalignment that only occurs in IE6.
I am not sure about how easy it would be to use ROR for the back end... It is possible, I am sure, since GWT ajax communication is just servlets. But they provide some really nice functionality for passing Java objects back and forth which you won't be able to utilize if your server isn't also using Java.
I wrote about some of the disadvantages of GWT recently. Mainly, the disadvantages are: long deployment cycle for changes to some parts of the application and a rather steep learning curve. As a seasoned Java programmer, the second should be less of a problem and if you use a seperate backend, the first is also mitigated (as a complete redeploy is primarily required when you change the 'server' part of the application).
GWT is a wonderful framework with lots of potential. Keep in mind that it's still quite new, though. There are some unresolved bugs that can really annoy you, and they usually require ugly workarounds to get past. The community is great but you'll probably end up with a few problems sooner or later that Google can't answer yet.
But hey, I say go for it. The potential for GWT is awesome, and I bet it's future will be bright.
You should definitely use GWT for a new project (it's pretty easy to use in an old project too).
I my experience it's very fast to learn and use. The compiled javascript code is much better than anything you could ever write by hand and it works fast too.
Another benefit is the ability to debug you're code (which is hell with javascript alone)
This blog has inputs from many experienced users of GWT and have some great discussion points. I personally have huge experience with varied UI Frameworks. I will add my two cents. Lets look at fundamental advantages and disadvantages of GWT
Fundamental Advantage
GWT takes the web layer programming to JAVA. So, the obvious advantages of Java start getting into play. It will provide Object Oriented programming. It will also provide great debugging and compile time checks. Since it generates HTML and Javascript, it will also have ability to hide some complexity within its generator.
Fundamental Disadvantage
The disadvantage starts from the same statement. GWT takes the web layer programming to JAVA. If you know JAVA, probably you will never look out for an alternative language to write your business logic. It's self sufficient and great. But when it comes to writing configurations for a JAVA application. We use property files, database, XML etc. We never store configurations in a JAVA class file. Think hard, why is that?
This is because configuration is a static data. It often require hierarchy. It is supposed to be readable. It never requires compilation. It doesn't require knowledge of JAVA programming language. In short, it is a different ball game. Now the question is, how it relates to our discussion?
Now, lets think about a web page. Do you think when we write a web page we write a business logic? Absolutely not. Web page is just a configuration. It is a configuration of hierarchical containers and fields. We need to write business logic for the data that will be captured from and displayed on the web page and not to create the web page itself.
Previous paragraph makes a very very strong statement. This will explain why HTML and XML based web pages are still the most popular ones. XML is the best in business to write configurations. A framework must allow a clear separation of web page from business logic (the goal of MVC framework). By doing this a web designer will be able to apply his skills of visualization and artistry to create brilliant looking web pages just by configuring XMLs and without being bothered about the intricacies of a programming language. Developers will be able to use their best in business JAVA for writing business logic.
Finally, lets talk about the repercussions in direct terms. GWT breaks this principal so it is bound to fail. The cost for developing GWT application will be very high because you will need multiskill programmers to write web pages. The required look and feel will be very hard to achieve. The turn around time of modifying the web page will be very high because of unnecessary compilation. And lastly, since you are writing web pages in JAVA it is very easy to corrupt it with business logic. Unknowingly you will introduce complexities that must be avoided.
You could also consider Grails ("Groovy on Rails") which gives you the benefits of a Rails framework and the use of the Java VM.
Our team recently asked the same question, and we chose to go with GWT, especially since the designer plugin made working with GWT more accessible to non-java experts on the team. Whoever makes this choice, just beware you DON'T use the GWT Designer plugin !! It has not been updated (in at least a year, apparently) to create a GWT application that is compatible with IE8.
Our team had almost completed our application layouts, which were working perfectly in Chrome, FF and Safari. Then they blew up in IE. IE 7 would load partial pages (but not composite includes), and IE8 was not even able to load up the application. It just hung.
The designer plugin has buttons that allow the user to add CellTable widgets that are not IE compatible (CellTable, DeckPanel, Horizontal Panel, Vertical Panel, among others). These will cause intense pain when the layouts have to be re-done in java without assistance from the designer.
Experienced GWT users love it, but the designer plugin will kill you.