Hi. It's hard to say without knowing the library requirements. Qt has no support for DOM, for example. So libraries which rely on manipulating HTML would not work. But other than that I think it should work.
More specifically, the two libraries that I tried (see links in the original question) use Immediately-Invoked Function Expression IIFE (maybe To Avoid Polluting the Global Scope):
// the code here is executed once in its own scope
The problem is that I couldn't call any of the APIs from my QML file. For example with the Backendless library, the code:
.import 'qrc:/backendless.js' as Backendless
var APPLICATION_ID = '...';
var SECRET_KEY = '...';
var VERSION = '...';
Backendless.initApp(APPLICATION_ID, SECRET_KEY, VERSION);
Fails with the message: TypeError: Property 'initApp' of object [object Object] is not a function
(this works when called from an html file in a browser)
I was checking its source code here
and you need to make some adjustments yourself. This library assumes that it's running either in a browser or in nodejs and relies on some of their features. It won't run out of the box, but it looks like one can fix it.
I'm not sure if you managed to get this to work properly, but another option to use Backendless is their REST API.
I used it, and it works very well. Most things are trivial, using QNetworkManager.