Wrap jQuery, dojo with custom library?

Wrap jQuery, dojo with custom library? - javascript

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.

Related

Is mootools alternative of jquery + backbone / spine / sprouteCore

I was full time java developers, now I also work on JavaScript. couple of years back when I started learning JavaScript, first library I tried was jquery like most of the people. But it made my life harder, and after sometime I started writing fairly large JavaScript app. It wasn't coming together for me using jquery. I had huge codebase without much of a structure. It was method blocks updating HTML blocks using selectors.
Then I tried mootools and obliviously as a java developer it appealed to me a lot. And I was able to write managible web apps having huge code base.
As per my understanding Mootools is not considered a preferred way to write JavaScript because it mimic conventional OO over default prototype-based OO language. So now to really understand javascript and desire of walking with the world, i decided to try other approaches, so again I turned back to jquery, and realise that only jquery is not enough. So started looking at current trending frameworks like backbone, spine, ember.js, sprouteCore. Strangly I found that these frameworks at their core tries to mimic conventional OO like mootools only by having constructors and creating a object of class and reusing this class object to create instance objects. So
Am I missing something?
Is mootools way really wrong?
Mootools project is very alive and releases new versions/features, but I don't
see many people talking about it on Internet, also there are no comparisions vs backbone/spine etc.

As per my understanding Mootools is not considered a preferred way to write JavaScript because it mimic conventional OO over default prototype-based OO language.
Where do you get that from? The greatest thing about javascript is that is so loosely typed (see what I did there) - you can write the same thing in a platitude of ways. There are also so many ways to abstract it and repackage it - and this applies from a simple new Array() vs [] to how you structure your app.
If you love JavaScript (or just know it and secretly hate it), you will be fine with MooTools. The API is mostly either native js or ES5 spec or - rarely - an extra utility that also feels 'natural'. The notable exception that stands out is Class. And the fact that you can abstract having to deal with prototypical inheritance by passing an object to a special constructor Type function that returns your instance is ... oh wait. It looks different but what it does pretty much sounds like normal javascript. Only easier -- why wouldn't you prefer that?
A lot is being made these days of the clientside MVC boom and this 'new way of developing apps'. Suddenly, jQuery folks were given the luxury of tap water! I have spoken to a lot of MooTools developers over this and (un)surprisingly discovered that most think MooTools rarely needs anything like that. I tend to agree with them. The only gaping hole is a view controller with templating but there are a fair few solutions.
The thing is, you cannot directly compare a MVC framework with MooTools, it is not the same. At all. You can compare the so called Model constructors vs Classes.
I have now spent a while researching various MVC framework solutions and patterns to see if our new app can be moulded into a 'best practice' shape.
Basically, I tried backbone.js (with and w/o a mootools adapter) and found it awkward to use after MooTools - it felt like a step back. When I say use I don't mean I can't use it but it feels awkward to extend and build on. I am sure it's just down to experience, though, have yet to read all the backbone patterns examples out there.
Typical issue I run into - wanted to have a special Model property that tells it to use localStorage to fetch/save. Not obvious how - examples tend to show you can either route Backbone.sync to one or the other but not both at the same time. I had to actually decorate the function and extend it, keeping the original referenced in case the model did not require localStorage. NOT the best / most obvious pattern to maintain and leaves me dependent on their changes not breaking my code.
In MooTools, I would have just extended my Model class and could have defined a custom Class Mutator property (like Binds or Implements). Done. Write what you know, they say, and not for nothing...
Another issue - it's tightly coupled with data and you cannot reuse models like classes - eg, a User model loads a user and renders through a User Edit view. You then want to create a new customer and suddenly, you cannot reuse the old object that easily and just render the same view but with empty values. I think it will also be down to inexperience on my part or bad architecture.
Ember.js I found slightly more moo-ish as an interface though It did not quite click either. Frankly, backbone was less trouble to setup.
There are other attempts. Composer is one - once again for mootools but it tries too hard to be backbone and is written by people that are relatively new to the framework so I would not call it mature. Knockout etc etc. There's a new one every day, literally.
Garrick Cheung released a framework called Neuro which has huge potential.
I wrote Epitome - a full MVP implementation based upon classes and events and wrapped in AMD modules, feel free to check it out. It also comes with a builder, documentation builder and many little goodies to get you started.
SeanMonstar released Shipyard, which is used by Mozilla Flight Deck - http://seanmonstar.github.com/Shipyard/. Whereas it's not native mootools, it's mootools-ish with mootools class etc - only w/o extending natives, so a great alternative.
BTW, try irc.freenode.net #mootools or the mail list and you will always get a good answer.
Anyway, enough on MVC. The points about MooTools have been made countless of times. Haters will be haters. Those that love it don't look back. If you are a programmer from an OOP background or are looking for something that renders itself well to patterns, do yourself a favour and stick with it. Exciting times are ahead. Roadmap for 1.5: AMD, for 2.0 (aka, Prime) Host object prototyping optional. These have been the two biggest talking-down points in the eyes of critics. No more 'dirty' prototypes so people can get on with using for ... in loops incorrectly on non-objects and without hasOwnProperty checks. Anyway...
Other things to worry about may be of importance. Like, the size of the 'community'. I think having a healthy community is a great thing but even if you look at jquery, the amount of actual contributors vs users is low. The ratio of quality CODE vs good looking effects is bad. The plugins you can use - a lot are not well written or dead and unsupported. When you draw the line, it's a lot less glamorous than you'd think!
I am not saying that mootools or other frameworks don't have these problems. It is fair to say MooTools people and especially the core devs are fairly private and less vocal about what they do. It may send the wrong impressions, I don't know. It certainly is no jQuery.
Ultimately - if you have the resources and the know-how, use what works best and what will scale. There are even these that use coffeescript and swear by it. Who am I to judge...
In the interests of full disclosure - you will find it MUCH harder to find a decent mootools dev when you recruit. Cannot be ignored...

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!

Supporting Multiple JS libraries

I have developed one of my modules using Dojo. Its gone really well and I have done a lot of custom plugins and server support in Dojo to allow AJAX calls, RPC + SMD communication with my server.
However, now that I am getting onto the user side of things, I am seeing that jQuery has some really nice already built plugins. Do you think it is possible to support both JS libraries realistically without it being a massive problem?
What kind of integration can I achieve? Does anyone have experience in this?
I have probably written somewhere in the region of 30k lines in Dojo for my Administration panel...

jQuery is very good about not messing with the prototypes of built in javascript objects (unlike Prototype), this allows it to be used with other libraries quite easily.
A source of potential conflict is jQuery's use of $ as a shortcut for jQuery. I'm not a dojo user, but if this conflicts with dojo in some way, there are instructions addressing this.
That said, I think you'd be better off looking at these jquery plugins and rewriting them and porting them to dojo. I'm sure the dojo community would appreciate it, and it would give you experience. It'd also make your application a little slimmer in the waist area.
Edit: I've noticed a couple answers trivializing the download speed of adding an additional library. I'd take this with a grain of salt.
As developers we tend to see only the extra 10ms it takes to download the library over localhost, or from our development server on a 100 Mbit LAN. The download speed is not so trivial from California to Virginia, or especially from USA to Europe. Additionally, it adds further burden on your client's javascript engine. If they are using a 1-2 year old good computer with Safari or Chrome, this would be negligible, but if they're on IE, FF2, or some versions of FF3 the difference can be severe, or at least measurable.

When using 2 libraries (both of which, I'm sure - were designed to be used by themselves) you have 2 main worries:
That one library will effect the other.
That having a dependency on 2 libraries will bloat your pages.
In this case, I would bet that #1 is not going to happen. Although #2 is still a concern.

Most of the popular JS libraries can be scoped to their own global shortcuts. JQuery can be set to not initialize the $ variable. JQuery aside, I hear that Dojo and Prototype can work together without conflicting.
Regardless of what combination of JS libraries you decide to use, the best way to get information on compatibility issues is to hit the mailing lists relevant to the JS libs you'll be using with each other.
http://docs.jquery.com/Using_jQuery_with_Other_Libraries
http://www.dev411.com/blog/2006/06/13/dojo-and-prototype-together

Query.noConflict() makes for fairly easy interoperability because you can redefine $. As hobodave draws attention to, Prototype is lousy in this regard (because you can't easily just redefine $ with Prototype). I am not sure but I think Dojo doesn't have any issues of it's own and plays nicely with others out of the box (please someone correct me if that's not true).
The biggest problem I've had is the number of "must have" libraries written in specific frameworks, such as for things like sophisticated graphing that would be non-trivial to implement from scratch.
Bloat is bad, but compared to image sizes JS script sizes are of negligible concern (because it's so small and connections are so fast and it's only on first page load if you get your caching right, it's almost a non issue). I'd say maintiainablity being more of a worry, and it's a matter of deciding if you want that must-have-plugin that you don't have the time or inclination to reinvent in whatever framework you are using.

I have used Prototype, jQuery, and ExtJS on several projects (for various reasons) and almost always use jQuery and ExtJS together. One way to limit trouble would be to avoid mixing libraries in any given page - keep Admin page to dojo and new pages to jQuery - but what fun would that be? :-)
I find few problems when integrating jQuery and ExtJS. I pick a framework for classes/objects/inheritance (I use ExtJS) and stick to it. Then, I use ExtJS to create most widgets and I use jQuery for low-level DOM manipulation and simple widgets. Again, I cannot recall running into conflicts when using two libraries, but FireBug is a good tool to uncover suspected causes of such conflicts.

Is there a general purpose JavaScript library out there?

We started a new project and realized that we needed a general purpose javascript library that contains a nice set of string functions, MD5, base64, allows extensions, etc. Also, copying and pasting functions from other libraries doesn't sound very attractive.
So, I guess the question is which javascript library contains the most general purpose functionality out there? or maybe there is a good collection of global functions out there we could use/extend. We know DOM manipulation is covered by many AJAX libraries including JQuery.
*Mind you, we could alternatively extend ExtJS, JQuery, etc. Is that what you guys are doing?

Google Closure Library
It contains (quoted from link):
a large set of reusable UI widgets and controls, and from lower-level utilities for DOM manipulation, server communication, animation, data structures, unit testing, rich-text editing, and more.
It also contains a nice set of string manipulating methods, in goog.string namespace.
Underscore
Underscore is a utility-belt library for JavaScript that provides a lot of the functional programming support that you would expect in Prototype.js
Underscore is intended to go along with other library, like jQuery or prototype.
It's not extensible like jQuery or Google Closure, though.

*Mind you, we could alternatively extend ExtJS, JQuery, etc. Is that what you guys are doing?
Yes, I do and I think most are. A lot of what you describe as a "general purpose library" is covered by Frameworks like JQuery, Prototype or Moo. And short of clipping the webmaster's nails, there's a JQuery plugin for everything that's not already in the core.
Still, I'm interested to see whether any other "general purpose" libraries come up here. There are fields - like string manipulation, as stated in one of the comments to another answer, and advanced date operations - where none of these frameworks is the holy grail AFAIK.

I use the jQuery library and a bunch of plugins. jQuery's plugin directory contains a lot of useful tools. There's also jQuery UI, a set of interactive components and effects, which you can use if you don't want to use a more complex library like ExtJS.
Of course every project is different, and you will probably end up writing some helper functions on your own.

I realize that others are going to say the same, but jQuery truly amazes me every time I learn something new about it.
DOM, CSS, and event manipulation along with easy AJAX, extensibility, and the plethora of existing extensions make jQuery a wonderful tool for web development.

jQuery is incredibly useful for UI manipulation. However, being open source, it contains some less than optimal code. If you start running into performance issues, don't be afraid to delve into the source and see what's going on.

I have been using jQuery for some time now and that seems to handle most of the basic operations I need. It has a healthy library of plug-ins and you can always write your own. It is a very good lightweight js library and even if it doesn't do all that you need it to you it is a good starting point.

Why is jQuery so widely adopted versus other Javascript frameworks? [closed]

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Closed 10 years ago.
I manage a group of programmers. I do value my employees opinion but lately we've been divided as to which framework to use on web projects.
I personally favor MooTools, but some of my team seems to want to migrate to jQuery because it is more widely adopted. That by itself is not enough for me to allow a migration.
I have used both jQuery and MooTools. This particular essay tends to reflect how I feel about both frameworks. jQuery is great for DOM Manipulation, but seem to be limited to helping you do that.
Feature wise, both jQuery and MooTools allow for easy DOM Selection and Manipulation:
// jQuery
$('#someContainer div[class~=dialog]')
.css('border', '2px solid red')
.addClass('critical');
// MooTools
$('#someContainer div[class~=dialog]')
.setStyle('border', '2px solid red')
.addClass('critical');
Both jQuery and MooTools allow for easy AJAX:
// jQuery
$('#someContainer div[class~=dialog]')
.load('/DialogContent.html');
// MooTools (Using shorthand notation, you can also use Request.HTML)
$('#someContainer div[class~=dialog]')
.load('/DialogContent.html');
Both jQuery and MooTools allow for easy DOM Animation:
// jQuery
$('#someContainer div[class~=dialog]')
.animate({opacity: 1}, 500);
// MooTools (Using shorthand notation, you can also use Fx.Tween).
$('#someContainer div[class~=dialog]')
.set('tween', {duration: 500})
.tween('opacity', 1);
jQuery offers the following extras:
Large community of supporters
Plugin Repository
Integration with Microsoft's ASP.NET and VisualStudio
Used by Microsoft, Google and others
MooTools offers the following extras:
Object Oriented Framework with Classic OOP emulation for JS
Extended native objects
Higher consistency between browsers for native functions support.
More easy code reuse
Used by The World Wide Web Consortium, Palm and others.
Given that, it seems that MooTools does everything jQuery does and more (some things I cannot do in jQuery and I can in MooTools) but jQuery has a smaller learning curve.
So the question is, why did you or your team choose jQuery over another JavaScript framework?
Note: While I know and admit jQuery is a great framework, there are other options around and I'm trying to take a decision as to why jQuery should be our choice versus what we use right now (MooTools)?

That's an odd question... I get the impression that...
you are very familiar with mootools and take full advantage of its OOP model, making your code easier to manage and support already.
you realise that jQuery's purpose is somewhat different and tweaked towards DOM manipulation and AJAX and that mootools does do everything jQuery does AND then some.
sounds as if you do not need to be using much in the way of 3-rd party plugins which makes the points of jQuery's popularity and support a bit less important.
Bottom line, is it the hype? jQuery is turning into one of these magical marketing buzzwords like 'AJAX', .NET and Web 2.0 — which is great for them but why do you need to justify staying with the framework that works so well for you? There's also the business considerations which I imagine will cover things like:
framework longevity, or is mootools likely to go away in the face of the ever growing jQuery — very doubtful, seeing as they just released 1.3 beta 1 and have 2.0 is in the pipelines for release by the end of the year.
cost of staff and their training (I imagine finding mootools programmers will be more difficult than these that slap jquery on their C.V / resume).
time (and cost) taken to maintain and extend your systems under each framework given your resources.
Both frameworks are great but I believe your interests are best served in staying with mootools.

Personally, jQuery does exactly what I need.
I try to do most of my stuff in my server-side code, which is well structured: it has proper OOP, layers, and an MVC architecture. When I need to do something with Javascript, I have found (so far) that jQuery has what I need. Frankly, that falls into three categories:
Simple DOM manipulation, usually showing/hiding stuff without hitting the server.
Ajax calls, nuff said.
UI perks, including modal popups, animations, fading transitions from/to hidden/shown. I am a hardcore backend coding guy, and I suck at UI stuff. I really like that jQuery lets me programmatically make stuff that looks appealing.
On top of that, the jQuery plugin library is huge, and I've found quite a few libraries that simplify my client-side work. Good stuff.
MooTools introduces OO thinking, which is nice, but not what I need. I want to keep my structuredness all on the backend, and not have to introduce that thinking to my client-side code. To me, client-side code is a very small piece of the emphasis and thinking about it from a Class-point-of-view is way overkill, and way more work. I feel like I'd be building two applications instead of one if I were to use what I'd think would be best practices for MooToools.
I think that sums up why its so popular, especially around here. By and large, we're backend code-y type people, and jQuery lets us make an appealing UI programmatically, and lets us focus on our backend core.

I'm not a fan of imposing classical object orientation onto JavaScript. There are so many ways to do it that one JavaScript Programmer might be using Base2 for OO, while another uses Prototype or Moo or JS.Class or Joose. Resig deliberately decided not to add classes to jQuery, and that has encouraged people to find more native JavaScript ways to solve problems.
As a result, it's easier for me to read JavaScript other jQuery writers write, and to write jQuery code that's easier for others to read. I typically don't try to emulate class OOP in JavaScript. Instead, I create objects on the fly and pass them around, and I have lots of arrays of objects. It's so easy to understand that I've even found myself carrying that thinking over to OOP languages!
For all I know Moo may very well have caught up with jQuery or surpassed it. But I can't spend my time tracking the 6 or 7 great JavaScript libraries to see which horse is ahead.
I think it's was largely a matter of timing. When masses of programmers jumped into AJAX, jQuery was the hot new cool thing that solved their problems.
Other libraries have largely caught up. YUI, ExtJS, Dojo, Moo--they're all great. But I can't use them all.
I work hard enough trying to figure out the ramifications of the new features of the library I do use. For instance, jQuery added Live events as of 1.3. This actually let me cut code from many pages. Does Moo offer that now too, and how am I supposed to know it happened, if it did?
I'm sure Moo is awesome. I'd love to have the time to learn it. But have you looked at Dojo? I had to use it on one project and found that it had pulled in most of the great ideas from jQuery as well. And it has pubsub and good support for Comet.
I sympathize with you. But your programmers are talking sense. Learning jQuery is good for their careers, and there are more books, examples, and fellow programmers to ask for help if they use jQuery.
If you decide to go jQuery after all, think hard before deciding whether to tack on an OO library. There are some cool ones (like JS.Class or Joose), but taking that step means isolating yourself from how most JavaScript programmers code.

I've been asking myself this very same question for a while now, by means of just trying to wrap my head around the argument. And with ever discussion I read, the overwhelming response has been "More widely adopted - therefore better".
I am one who uses both extensively. JQuery at work (adopted because it was "more widely adopted") and Mootools on personal projects. As a result, I constantly find myself feeling crippled when using JQuery; Be it with JSON support, element creation, event handling... and so on. At work, I find myself writing chains 75 events long... and I feel dirty as a result.
My main overall beef with JQuery though, is that there's a lack of consistency or practice where plug-ins and 3rd party developers are concerned. The anecdotal "More plug-ins are available" really doesn't help me when there's no consistency between the plug-ins, structurally or otherwise. It took me several weeks to learn the "accepted" plug-in model, and even then, I've adapted my own pragmatic style into it, as I find error and inefficiency within the current structures. It can be said that it's a 'Pro' that anyone can jump in and start JQuerying it up. However, I am more inclined to call that a 'Con', in that you will see 30 different ways to accomplish something, and it's difficult to pin an accepted standard.
So what does it mean to "Know JQuery", Does it mean you know how to rock a little .hide().show().fadeIn().fadeOut()?
When I have to get gangster on my JS at work, I miss me some Mootools. I mean no Native JSON support? C'mon......
In response to the "Widely adopted" response, we all know OSCommerce is the most "Widely Adopted" shopping cart, and we all know what a pile of shit that is. I'm in no way comparing JQuery to OSCommerce. I'm simply pointing out the faulty of "Widely Adopted" response.
As for plugins, the App store for apple has what... 100k apps? 50,000 are fart apps. Sure there's a lot of plugins to JQuery, but the ratio of trash to worth-while is great.

jQuery gives you access to crisp and concise functional programming methods. Since the release of method chaining in (LINQ) in C# 3.0 this works very well for .NET programmers. So the flow from one language to the next is easy. To be able to query the DOM for an object, or a list of objects, works much better for us. It is jQuery's selection power first that makes it so attractive, then the extendability of it, and of course all the built in features that come with it are nice. Also, the community behind is wonderful in that I first look to see if someone else did something and then attempt to do it myself if a solution was not found. And last...but certainly not least...the fact that Microsoft is going to include in in Visual Studio 10 and support it is great. Moo Tools, Prototype, etc. just can't compete with all of the above.

JS frameworks are so much alike, anyway. If you've been working with mootools for some time, stick to it. Knowing your framework is much more important than choosing one because of this or that.
In my opinion, mootools is better for advanced javascript programmers, while jquery is better for non-javascript programmers. That's what I think after reading both documentations, mind you, I didn't use any of them. jQuery lacks support for the core of javascript, function binding, object cloning, thread stacking, to name a few.

jQuery, like any framework, does what it does and if it doesn't fit your needs you should use something else. I don't use jQuery to do complicated programming in javascript, I use it because it makes DOM manipulation and CSS3 style stuff simple and 95% of the time that is what I need.

I have not looked at MooTools in a while either. But here are my points for JQuery:
Consistent programming model (there is a JQuery way that works)
Excellent documentation. When I started JQuery had the best documentation out there.
Extensive 3rd party plugings
Microsoft support -- I am an asp.net developer, this helps ease clients minds. Plus it ships with my tools now.
Lots of getting started guides.
JQuery's website looks nicer than MooTool's web site. I'm sorry that matters, but it does. Remember, many of these tools need to appeal to designers as well as developers.

YAGNI.
Yes, it's kinda out of place here, but that's the main reason jQuery has a larger base than MooTools. All those extras MooTools brings to the table are nice, but YAGNI.
It's not about best, it's about satisficing -- finding the adequate solution to the problem at hand. jQuery is easy to use, its primary aim is DOM manipulation. Since 95% of the people picking up javascript are doing so just to manipulate the DOM, there's no point in going through the longer MooTools learning curve. MooTools simply doesn't bring anything to the table for them that jQuery doesn't deliver with less effort.
MooTools demands more from you before you use it, jQuery lets you throw something together quickly. If you start writing large, heavy-duty js apps, you might run into some of the drawbacks of that approach, but again 95% of the folks writing js don't do that, so those things don't matter to them. They use a server-side language for the heavy-lifting and javascript for the DOM.
For that matter, they may not matter to your team, either. To take you through the lists, point by point (jQuery first):
Large community of supporters -- only slightly relevant to the project. Of more relevance to the team personally, because it speaks to life after you. If misfortune strikes (please, God, no) and your firm is gone, jQuery gets them more jobs than MooTools.
Plugin Repository -- very relevant, as it helps keep from reinventing the wheel.
Integration with Microsoft's ASP.NET and VisualStudio -- very relevant if you're a .NET shop. In fact, this alone should be the reason to switch if you do .NET.
Used by Microsoft, Google and others -- who cares?
Now for the MooTools list:
Object Oriented Framework with Classic OOP emulation for JS -- irrelevant, unless the nature of your projects makes that a plus. I don't know what you're building, but for web shops, this is only rarely relevant. Most web shops don't have enough code to make this a plus.
Extended native objects -- again irrelevant for most web shops
Higher consistency between browsers for native functions support. -- Relevant
More easy code reuse -- This conflicts a little with the jQuery advantage of a large repository. A large repository by itself speaks to reusing code. I suspect you're using a narrow definition of code reuse, here, that may not be relevant. I've reused a lot of the jQuery code I've built, as well as MT code.
Used by The World Wide Web Consortium, Palm and others. -- Irrelevant. The only relevance about who else is using what is if you're wanting a job there. There's more relevance in how many shops use it than in any particular shop using it.
There is no One True Way to approach javascript coding. Get your bias out of the way, and sit down with your team and get their bias out of the way as well. Talk turkey about the specific types of projects you're undertaking (and want to undertake) and the strengths of each library as applied to those cases. (How they might handle other cases doesn't matter, because those other cases don't exist.) You should arrive at a consensus from that.
(YAGNI = You Ain't Gonna Need It, if I need to explain it.)

I choose to use jQuery as our default UI library precisely because it does not extend or otherwise monkeypatch native objects, unlike prototype.js or mootools. Kick in the documentation angle and there really is no question as to which framework to use.

You kinda say it yourself:
Given that, it seems that MooTools does everything jQuery does and more (some things I cannot do in jQuery and I can in MooTools) but jQuery has a smaller learning curve.
Most of the extra stuff that MooTools does is stuff that we just don't need.
As you say yourself jQuery is easier to learn, which is actually more important for most people when choosing a framework.

What I DON'T need in JavaScript is definetely OOP and some ugly object emulation.
Last time I checked MooTools (maybe 1,5 years ago :-), it had browser incompatibilities with manipulating multiple select.
So jQuery is completely looks OK to me.

Not only is jQuery a nice library, but its creator, John Resig, also has some street cred as the author of Pro Javascript Techniques.
We have 2-3 copies of this book around our office.
jQuery is small (intentionally so) but can have functionality added to it through plugins.

The thing that made my experience with mootools a rather unpleasant one was the documentation and the stability of the API:
I simply wasn't able to find a documentation that related to the mootools-Version in use. Won't be that much of a problem if the API defined was stable. But due to some functions that disappeared in the newer Version (a ChangeLog was found after hours of searching) a migration wasn't possible either. After that, mootools was out of the race for me.
Like many others, I don't want to introduce class-based OOP into simple user-interface manipulations. Thats what I use jQuery for: not so complicated user-interface stuff.
When I have to build rich browser-side applications, I'd always switch to the big solutions (ExtJS, YUI, qooxdoo) that offer a variety of ready to use widgets.

Larger User Community and more wide-spread adoption makes a big difference when comparing tools/libraries that offer similar functionality and concepts. Larger community means more support, more examples, more good ideas, and more reusable code snippets, which is especially important when you're working on a rare scenario -- more likely someone else has encountered it before.
Secondly, in benchmarks I've seen, jQuery is faster than MooTools.
I also really like their emphasis on keeping a small core and adding functionality through plugins. Prevents the core library from getting really big and unwieldy.
I've never used MooTools personally but I have no doubt that its a fantastic library that offers some acceptable equivalent to most any jQuery feature or concept, but point #1 takes the cake for me.

Another reason: It's easier to sell jquery to management. Doing internal, asp.net based developement in a corporate environment the magic words are "it's supported by Visual Studio".

For one thing, that's not all it does. There are quite a few other features as well. For another, not everyone uses it. But I don't want to interrupt a good rant.

I have to second a lot of the answers...great documentation and community support is crucial. I used to hate js programming and would avoid it like the plauge, but now I've completely embraced it because of jquery and the quick learning curve.
It's not always about who has the best technology!

Mootools, does not function properly or does not function at all when using jquery prototype etc. Agreed there is absolutely no reason to use them simultaneously, but once in a while they do land up on the same page (ex. plugins, slideshows, widgets etc) and things stop working.
That in itself is unacceptable. So all props for jquery to not create unnecessary headaches!

Why did people start using fax machines? At a certain point the benefit increases exponentially.

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