Mootools, Scriptaculous, Prototype, YUI or JQuery?

[eluser]Nick Husher[/eluser]
[quote author="Michael Wales" date="1201247117"]lol, every week this questions is asked

Every week, the answer is jQuery[/quote]

I disagree; the answer is always, "Choose the one that works best for you." JQuery is a good solution, but it would be vastly oversimplifying the issue to say that jQuery is the answer to the OP's question.

As I have always commented in these threads, I'm a huge fan of YUI. To me, it most represents what I think of as responsible programming. The framework is unobtrusive, doesn't damage the global namespace, is very feature complete, and is extraordinarily well-documented (the non-beta components, anyway). In many ways, YUI resembles the Java API; it's big, it can be a bit intimidating, and has a somewhat-larger footprint than other options. Then again, it offers some awesome stuff right out of the box and is trivially easy to extend 'properly.'

1) Which of the JS frameworks is the most compatible with all browsers, in all operational systems?
YUI has a Graded browser support list. Anything that's listed as "A-grade" is fully-supported by YUI. This includes a rich text editor, which as I hear it is difficult to do in Safari.

2) Which of them downgrade nicely if the user have disabled Javascript?
This is really up to you, regardless of the architecture that you use. You can make your site work without Javascript happily, then layer the JS on top of it, or you can force the user to have JS enabled to make anything work at all. Unobtrusive javascript is possible without any frameworks at all, but is made easier by just about all of them. YUI has a wonderful event handling system, which seems to be the biggest point where unobtrusive scripting breaks down or becomes difficult.

3) Which of them loads and runs faster even in old and slow computers?
I've run YUI happily on a 900mhz system with 256m of RAM running WinXP, Apache, and a few other memory glutton programs. The animations were a little choppy (8-10 fps rather than 40-60fps), but otherwise worked fine.

4) Which is more customizable and let us to enable only what we want? Which able us to use only the basic AJAX functionality or only the effects we really need?
YUI has a core that contains functions related to Javascript language concepts (type checking, browser detection, inheritance, etc), events, and modifying the DOM tree. The core is basically required to do anything in YUI and weighs in at 32kb. Everything on top of that is basically optional; connection, animation, dom tree querying, json, image loading, and the like are all independent of one another. You can even load modules on the fly as you need them, which can be very handy.

5) Which of them simplify the task on the server side, instead of force us to build the remote PHP scripts more complicated? Which standards/protocols they use: JSON, XML, DOM, etc?
YUI has a built-in safe (as opposed to using the eval function) JSON parser. XML is supported by virtue of XMLHttpRequest. You can also just send plaintext over the wire and use that to insert into your dom tree.

6) Which have clean code and intuitive use of classes and functions, and also a very good and complete documentation?
YUI's non-minified source code is extraordinarily clean and well-documented.

8) Which have the major list of effects, but also useful things like form generation and validation, field mask/format, calendar popup, color picker popup, HTML editor, etc?
YUI has no built-in special effects, but has an intuitive animation utility. It's very easy to make things slide, fade, move along bezier paths, change color, and do so by various mathematical curves (nonlinear animation). It has a calendar utility, color picker, and HTML editor as well.

9) Which have the best team behind it and the best community? Which have the best support?
YUI's programmers are some of the best JS programmers on the planet. Douglas Crockford is one of the primary proponents of Javascript as a real programming language, and spearheaded the effort to get people to use JSON rather than XML. He was one of the first to document specific code conventions to allow classical object-oriented patterns inside of Javascript (private, static, and public variables/methods). Dav Glass spent months working out the event handler problems in Safari to get the YAHOO RTE working. Other projects, such as the Datatable control, or the Charts engine ooze quality.

The community is much smaller than that for Prototype, Scriptaculous, or JQuery.

10) Which is the most used by web sites around the world? Which is the most known by developers?
Probably Prototype or JQuery. Or something in-house.