About ExtJS, once I heard Shaun McCormick (aka splittingred) said that ExtJS has been choosen for backend manager because it's OOP feature. I myself agree with that. You can look at another javascript framework, but no one can match ExtJS in terms of OOP. ExtJS is the most complete and extendable OOP framework, and that really help the development and perfectly fits with MODx.
jQueryUI does not abstract you from HTML. I don't want to know about HTML when I write my app/component. And I want to easy dynamic creation/destroing of components. Yes, ExtJS generates heavy DOM structure, but this enables flexibility and power of components.
I hope we get cool canvas-based fast frameworks in future, but now we have to use slow DOM frameworks.
For future app-oriented frameworks AngularJS looks really nice...
I'm sorry, you want to write an app/component running on the web without knowing about HTML?
var button = document.createElement('button'); button.innerText = 'My button'; button.id = 'button1'; button.addEventListener('click', function(){alert('hello!')});
ExtJS, qooxdoo etc provide all that a developer needs. I just want to focus on programming my extra, I don't want to know what my components use for rendering - div, span, canvas or svg.
HTML initially is not designed for writing apps, so this lacks of many things , that developer needs. Such libraries as ExtJS eliminate these whitespaces...
[Developers building the DOM directly and not using markup] is a clear distillation of what scares me about the road we're headed down because for each layer you throw out and decide to re-build in JS, you end up only doing what you must, and that's often a deadline-driven must. Accessibility went to hell? Latency isn't great? Doesn't work at all without script? Can't be searched? When you use built-ins, those things are more-or-less taken care of. When we make them optional by seizing the reigns with script, not only do we wind up playing them off against each other (which matters more, a11y or latency?) we often find that developers ignore the bits that aren't flashy. Think a11y on the web isn't great now? Just wait 'till it's all JS driven.
I hope we get cool canvas-based fast frameworks in future, but now we have to use slow DOM frameworks.