What are the implications of node.js? - javascript

I've been reading about node.js lately. I've seen many articles about how it's really great and all from some prominent people. Given the inertia that this project seems to have, and that I am currently learning javascript and jQuery, the project has gotten my attention. I get that many people are excited about it, but I don't quite understand what the implications are.
I understand that it is event driven and non-blocking and all of that, but where I'm confused is in regards to its intent.
Does node.js mean that we now have a foundation to run Javascript on the server-side, so that later maybe someone will create the Ruby on Rails or ASP.NET MVC equivalent for node.js/Javascript? Perhaps there already are web frameworks out there, but if so I haven't heard the hype machine yet.
I hope my question is clear.

I think the major implications are two-fold: huge performance and scalability gains, and the possibility of creating web applications where two or more people may work on the same web application at the same time, watching what the others are doing, in real-time. This latter one not only has big implications for web-based gaming, but also collaboration tools, etc.
It would appear that node.js is exactly what the real-time web needs. For that kind of thing, be sure to also checkout Socket.IO, which achieves cross-browser HTML5 web sockets. Combined with node.js, this makes for an incredible platform.
Check out what was made at the node.js knockout for some examples of what can be done.

I think what you can hope for is going to be more like twisted for Python, rather than e.g. rails for Ruby -- a rich, powerful framework, but still one requiring skill and care to use properly, because asynchronous programming is always like that... it's the price you pay for its absolutely awesome performance potential.
There are and have been Javascript server-side frameworks, but with server-side Javascript never being a really popular option, such frameworks never got the "critical mass" of support and enthusiasm that, say, jQuery has, or rails for ruby on the server side of things.
I doubt async programming (with its subtleness and difficulty) will be the defining trigger for a "mass movement" (hey, I hope I'm wrong, but I see e.g. the relative popularity for Python of Django, with none of the awesome performance, compared with Twisted, with _all_ the awesome performance... but the intrinsic difficulty too!-).
OTOH other developments (such as, simply, the wide availability of powerful, high performing, solid Javascript engines like V8) are more likely to eventually result in wide availability of (non-async;-) server-side Javascript choices, and as a consequence the possibility of the development (or porting -- e.g., a framework like dojo could already offer a lot to a JS server-side app, only parts of it are actually client-side) of powerful, simple, and therefore eventually popular framework. Nevertheless, I wouldn't hold my breath waiting for that either...

Node.js is an application server, not yet another webapp server. As the article says, it saves you the trouble of writing the event loop and using two languages to write apps (python/java/ruby/php backend, js frontend). As it is based in the V8 Engine by Google it's really fast and has a low memory footprint.
There's a web service framework called GeddyJS, and Node.js comes with a set of libraries for IO, database and math. It's also possible to extend it with addons, though last time I checked documentation was still a little rough on that.

There is a node framework called bogart which you can easily use the MVC pattern and mustache or common-ejs for templating.
http://github.com/nrstott/bogart

Related

Can I use JavaScript instead of PHP, replacing Apache with Node.js?

Can I write my web-site only in JavaScript being sure that my code is concealed from anyone? In this respect, is Node.js, like Apache, can be given access to through an Internet-provider?
The answer to both of your questions is yes.
Node.js can completely replace Apache (assuming you are willing to re-write all of your PHP as JavaScript). If you have your Apache running in reverse-proxy mode between your server and client, you can even handle some requests in Node.JS while handing others in PHP. This will allow you to maintain original functionality while changing the code out, and also allow PHP to handle more mundane tasks.
While you cannot prevent raw JavaScript from being read through any means of obfuscation, you can prevent people from reading your code by note making use of standard JavaScript at all. You can use a NativeExtension for Node to add an extension handler for encrypted JavaScript files:
require.extensions[".jse"] = function (m) {
m.exports = MyNativeExtension.decrypt(fs.readFileSync(m.filename));
};
require("YourCode.jse");
This will convert your JavaScript code to a .jse, which you would then package for production. Considering the encryption is done inside the native extension, the encryption key wouldn't be revealed.
Hope this helps! :)
Yes, you definitely can. It may, however, take a while to transition existing code, and if this is for a corporate institution, you'll have to ask your coworkers and your boss/supervisor. Good luck, and remember, always document your code in JavaScript (no types) all languages.
NodeJS is much faster: http://www.hostingadvice.com/blog/comparing-node-js-vs-php-performance/
Many more libraries: http://npmjs.org
Only need one language for everything
Comparing PHP with another technology like Node.js which is meant for an entirely different type of task, comparer must mention the difference of use-case/context in which one is suitable over others.
Let's talk about in terms of a different area of execution because we can not Disgrace any of them and both have its own priority.
If you talk about in terms of Application Domain.
PHP :
CMS (Content Management Systems) like WordPress, Drupal also use PHP which makes it possible to be used in creating blogs, websites, e-commerce sites, etc.
Used in developing CPU-intensive applications like meteorology applications and scientific applications.
should be used in applications in which the client does not have to interact with the server again and again
PHP 7 is based on the PHPNG engine that speeds up PHP applications more than the previous PHP interpreter (Zend Engine 2.0). Thanks to PHPNG, your apps see up to the 2x faster performance and 50% better memory consumption than PHP 5.6.
NodeJs:
Nodejs is ideal for developing highly scalable server-side solutions because of its non-blocking I/O, and event-driven model.
Used massively in Real-time applications like chat applications, blogs, video streaming applications.
Used in developing single-page applications like resume portfolios, individual websites.
Node.js should be used for the applications which require a lot of interaction between client and server.
For some tasks, Node.js may be faster than the “standard” web server with PHP because it runs as a single thread with non-blocking IO for each connection, hence there is no memory overrun. Due to this, Node.js is useful when there is a need to process data in real-time (chats, games, video, big data streams without logic)
PHP is Still alive and he has learned its lessons from Node.JS
ReactPHP enables developers to write PHP-based socket server to process requests constantly as well as Node.js does it (yes, Node.js is faster, but the fact is that PHP can also do it). The same thing with Workers (the classes responsible for running asynchronous jobs and synchronizing their results) or Amp (libraries that are used for writing non-blocking asynchronous code). Hence, it is easy to create long-running processes using PHP. Additionally, there are a lot of tools for supporting and managing these processes (such as supervisord).
So, the same tasks may be performed either with PHP or with Node.js. The question “what tool to use” is a question of personal preferences. you can use Node.js for tasks involving big data flows and PHP for tasks involving complex logic, high-load tasks, for dealing with external utilities, applications, and OS.
From the scalability perspective, there are no big differences between PHP and Node.js, it is more important to consider the project’s architecture.
Dayle Rees (a Laravel Framework contributor and developer): For a long time PHP was the butt of many language jokes, but I honestly feel that it’s becoming not only a popular language but a powerful one. PHP7 is great. The speed boost is one thing, but having optional support for full type hinting is a game changer. We’ve also got modern tools like Laravel and Composer, breathing new life into the language and its supporting community. With this in mind, I think it’s unlikely that Laravel will move from PHP. I think it’s more likely to gain further integration with front-end tools to provide a complete application building platform. That’s where I see it heading in terms of future expansion. I’m sure the Node will continue to excel when dealing with microservices and threaded applications.
The most important and most awaited News from PHP is, PHP is scheduled to receive a Just In Time (JIT) compiler in its next major version PHP-8 (most probably in sep-2021).This is going to boom the php and it breaks all his limitation due to JIT.
Wrap up
To wrap up Both have some pros, both have some cons but the amazing thing is both are created by intellects to make the web development better. While selecting the technology the question shouldn’t be which one is better but which one can serve your project needs in a better way. Understanding your project and business logic can give you a clear idea about selecting the right technology for your project.Moreover, one more important thing to consider is the skills and proficiency of the developers using the technology, how they use them and apply to the project.

What is the difference between Cappuccino and Node.js?

I have been working with node JS for about two weeks and I am liking it a lot. I came cross something called Cappuccino; it sounds like what I want to use to develop a web application. As a beginner, can someone assist with explaining what exactly Cappuccino is and how it fits into node?
Really my hold up with developing an application is that I come from a VB background and I am use to forms to design my desktop apps. I do not want to be limited with a WYSIWYG type of IDE, that is why I started with node.
What sort of web application? There are... many JS libraries/frameworks. It's a jungle.
My strong advice is to build several things, from very small to less small, using pure Javascript. Otherwise you will, I promise, remain forever cloudy on what the language is vs. the frameworks layered on top. JS is very mutable and frameworks have a tendency to create new semantics on top of the core language. The downside of learning by using these is you ever fully understand the complexities and subtleties of the language itself, nor do you ever really understand what those frameworks are giving you (in many cases, things you don't need or that artificially constrain you). Be wary of framework entanglement.
As you get used to writing simple scripts in a text editor (try Sublime Text if you want something much better than that), you'll begin to appreciate when and why you might want help from a framework. Move on to jQuery, as it's the most widely used library and is either a dependency or heavily informs the style of many other libraries out there.
I'm working on a blog post about the topic of frameworks, by no means comprehensive as there are hundreds of them it seems. Specifically, breaking down about 20-30 major players by their intended domain (e.g. DOM manipulation, Single Page Applications, data-binding, MVC, etc.) and strengths and weaknesses.
There are some great books and YouTube videos going into many aspects of modern JS. Anything by Douglas Crockford I recommend (especially book or video "Javascript: The Good Parts". He's pedantic but wise and generally on the money. Then for more inspirational stuff about recent/upcoming changes to the language, watch some stuff from the Google I/O events. Check out HTML5rocks.com for articles on some cutting edge features available in the browser. There are many many more resources, but these are some good ones.
Oh and be sure you are familiar with the dev tools in the browser. I personally recommend Chrome as best of breed. Learn the keyboard shortcut to open it on any page, inspect, and noodle. There are some fancy things such tools support like live editing/saving of source, profiling and debugging, DOM/CSS inspection, and on and on. There are other free and non-free IDEs but IMHO they are too much overhead for someone just learning (and many advanced JS developers use Sublime Text).
P.S.: jQuery, per its design goals, is still going strong but is aimed for obsolescence as browsers increasingly are converging on true standards (ES5, HTML5, CSS3). Even so, for many apps, its shorthand semantics are much better than even the newly supported standards for many things. And it's not going away any time soon, just becoming less important. Like IE. Ignore IE unless you need to build things for work.
As far as I can see, Cappuccino is a client-side framework of some kind, in the same kind of vein as Backbone.js or Angular.js, and is in no way comparable with Node.js. They run in completely different environments (Node on the server, Cappuccino in the browser).
A client-side framework like Cappuccino would be used to implement web apps that needed to do a lot of work on the client side. For instance, if you implemented a real-time web app with Node, you might use it to simplify inserting new content into the DOM.
I haven't used Cappuccino, and it doesn't seem to be all that popular. It seems to be squarely aimed at people with a background in Cocoa development on Mac OS X, so if that's not what you're after I would recommend you look elsewhere. Client-side MVC frameworks are very useful for some use cases, and the big four seem to be Angular.js, Ember.js, Backbone.js and Knockout.js, so I would check out one of them before considering Cappuccino. Knockout is very easy to learn, but lacks routing, which was a deal-breaker for me, so I switched to Backbone. Considering how much mindshare it seems to have, I would probably now go for AngularJS.
Cappuccino is a client side framework built on top of Objective-J which in turn is a complete language built on javascript. It's intended solely for building desktop class applications that happen to run in a browser.
Objective-J adds features to javascript (like classical inheritance) in the same way Objective-C adds them to C. You can use Objective-J with node but probably not most of Cappuccino. Cappuccino is the framework that lets you build rich user interfaces in a way that allows you to completely ignore that you're working with html.
I would not recommend Cappuccino as a first foray into web development unless you really only want to build a business application and you are already a proficient Mac OS X or iPhone developer. It will not help at all to teach you about the web.
Cappuccino is (imho) head and shoulders above everything else in its league, but it is intended (or most useful) for a very tiny niche.
If you're still interested in Cappuccino (or Objective-J) you should really check out the learn section of the Cappuccino project website

Need help determining how to approach building my project

I'd like to create something similar to a family tree online app (like geni.com). I'm unsure what languages I should use to build it with. My IT strong points aren't in programming and this project is going to require me to sit down and learn some languages. My problem right now is that I don't know what languages I should use.
So with the idea of a family tree online app in mind here are some of the specifications.
- I do not want to use flash.
- The app needs to be zoomable and scrollable (sort of like google maps)
- The app needs to be able to add content without reloading the page. Perhaps there's a little "+" sign and when I click it, I can add a tag/title/description/picture
- The app needs to be able to save your work for that user to retrieve later on.
- The layout that a user is able to create in is sort of widget based where the user can add a new bubble and then in that bubble they are able to add text or content.
I started programming this with HTML5 canvas and Javascript, but I'm stuck on creating a connection to the database that isn't directly from Javascript (because that seems very insecure to me). But I'm not just stumped on how to interact securely with the database (I don't even have a database picked out), but also I'm concerned that I won't be able to build out the app with just javascript and may need something else like ajax or something but I'm unfamiliar with what each language does nowadays.
If you are starting from scratch, then the best language to use is the one you are most comfortable with. Alternately, if you don't plan to be developing the whole thing yourself and you already have some other interested parties on board then the best language to use is the one that the majority of you are comfortable with. If it's just you and you do not yet have any favorites, then look around and play with a few - it's the only way to find out if you will actually like / be effective with them.
That being said, a few of the more likely candidates these days are:
JavaScript: Long gone are the days when this language was simply a way to put the D in DHTML. These days JavaScript is a viable client and server-side language. (Others here have already recommended Node.js -- I'd also recommend NPM (node package manager) to handle your dependencies). With a little bit of planning you can reuse most of your application code on both the client and the server side. On the downside, most of the server side technology is very new (only a few years old at most) and so you may find yourself implementing tools for use in your application rather than your application itself. Finding servers that support it will also be harder, again on account of it's age.
Perl: At the opposite end of the spectrum of age, we find Perl - the first commonly deployed language used to make web applications it still powers a great variety of useful websites out there (include new ones such as Pinboard.) The tools that are popular on CPAN have been vetted under fire. The good news is that it is not going anywhere anytime soon. The bad news is, you might have to search a little harder to find a module that supports [that newest, baddest thing that just came out yesterday].
PHP: The BASIC (or Perl, depending on who you ask) of the modern web, PHP was designed from the ground up to do one thing - make building dynamic web pages easier. Its popularity means that there is quite a lot of server support (PHP + Apache + MySQL is the Model T Ford of web servers -- everyone can afford one) and an enormous amount of pre-built code available for perusal. However, like BASIC, PHP's strength is also its greatest weakness. Almost anyone can write something that works in PHP ... how well it works depends on who wrote it. The caveat emptor that applies to all code snippets found on the web applies in spades to snippets of code written in PHP.
Python: The language that made programing fun again (at least for those who can see past the significant whitespace and lack of blocks / anonymous functions and overlook < 3.x's issues with non-ASCII out of the box.) It's a general-purpose, flexible and multi-paradigm language with quite a substantial standard library (but without .NET or Java's incredible bloat). In addition, quite a large amount of work has been done in it, so there is a good chance that what you need has been already developed by somebody else. Plus, it can make you fly.
Ruby (with or without Rails): The language that made the web fun, coupled, if you so desire, with the framework that made MVC cool. There is lots of documentation out there, and a great community, with many prebuilt tools (called gems) from which to pick and choose - free and cheap servers are not as common as their PHP counterparts, but they are likely to be of higher quality (when chosen at random).
All that being said, they are all great languages for web development. What matters is not what we think you should use ... but what you are most likely to be effective with. All of the languages listed above are mainstream (or will be in the next two years), easy-to-learn and easy-to-write languages. You cannot go wrong, no matter what you choose to start off with.
Alternately, if you want something a little more difficult, or less mainstream ... I am working with .NET applications at work, and with Lisp (SBCL)-based services in my spare time. I have heard great things about Lua and Java too ... there are at least two C++ web frameworks out there ... and I'm sure that there is somebody is having fun building a web service in COBOL with a FORTRAN backend. ;-)
As someone has already pointed out, you will need to work with a server side language as well. (Ruby, Python, PHP) You are exactly right there you should not be attempting a database connection via javascript in the browser.
You'll need to build out a server side application to handle the basic operations of your application.
I'd strongly recommend reading up on the MVC design pattern, and possibly looking into Ruby on Rails as your backend framework, it plays very nicely with ajax like features, and has a somewhat shorter learning curve, I believe, than some other frameworks / languages.
You will need server side scripts in a language like PHP or Ruby on Rails to interact with a database.
If you're already familiar with HTML5 and JavaScript, may I recommend using Node.JS? It's about the closest you'll get to what you already know with browser development. It can also hook in with database systems which are closer to the HTML5-suggested IndexedDB.
with that in mind...
If you're inexperienced with programming and programming languages, then the app you describe will involve a pretty big learning curve. While Flash and Flex have really nice interfaces to build apps with click-and-drag, the tools for HTML5 are much less mature.
That's not saying it's not possible with HTML5. Just that there's still some time to wait before people create tools to bring the app building process closer to what Adobe provides.

What are some architectural reasons to use node.js aside from scalability?

The most common theme I read about why to use node.js is for high scalability due to it's evented, non-blocking I/O model. I'm trying to understand other non-scalability uses cases (and aside from being used as a general server-side javascript engine).
Does node.js have other use cases if scalability isn't a concern of mine?
If yes to #1, what are they?
Is node.js usage appropriate for any particular type of application architectures? E.g. similar to how some key/value (nosql - ugh I hate that term) databases are useful other than for scalability reasons.
My reason for trying out node is the fact that it is incredibly easy to send JSON data between the server and the client for ajax requests.
If you use something like MongoDB, which stores data as JSON object too, you never have to worry about translating or parsing your data.
If your site uses a lot of ajax, and you're sending your data as JSON objects (rather than XML or plain text) then node.js will save you a fair bit of effort.
I think this blog posts sums it up quite well:
http://debuggable.com/posts/understanding-node-js:4bd98440-45e4-4a9a-8ef7-0f7ecbdd56cb
In short (pro node.js):
Speed
Javascript (especially if you know it already)
Efficiency
node.js is really great. Give it a try! :)
I can think of one reason, but its not very deep. Basically, If you are developing an RIA, your entire stack can be javascript. That might have some value.
But Ill question my own answer, namely the thought is, even if it makes the server side code more accessible to client side developers, they still need to understand how their server stack works. So there is still some learning to.
To be accurate, I think the general server-side JavaScript engine in your question would be V8, while according to its creator Node was built for "scripting network programs."
Based on many of his comments I don't believe he views it as broadly as many of us do, but recognizes where it can go. [I can't speak for anyone else--that's just my interpretation based on the writings and presentations I've seen.]
So it approaches things from a somewhat lower level, makes HTTP a first-class citizen and just happens to be really cool, which I think makes it enough of a "use case" for most of us. ;)
It does have a learning curve and isn't the most stable platform to build on due to its rapid development. I believe time will tell where it's most useful.
For now people are using it for "real-time" apps due to its lightweight, asynchronous nature, as well as general Web development, though IMO its sweet spot remains with its originally stated purpose.
What I like about node.js aside from non-blocking I/O model, scalability and all that "primary reasons" stuff:
Lightweight nature of it's framework. Basics are easy to learn.
Developer community building tons of useful modules and libraries on github which are expanding node.js lightweight core and it's capabilities.
It's really easy and fast to build server side and real-time systems (for example http or socket based) without the knowledge of complex libraries.
I like to use NodeJS to write testing harness because you can write a stub/server/client really quickly. And you can drive your application, with ease. I can easily script a third party back-end server to do performance testing on my application. I also use it to drive my application. I can perform complex client server scenarios using setTimout to cause multiple events to be trigger based on any logic I want and test them at scale.

Should I use Google Web Toolkit for my new webapp?

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.

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