Where to get interesting, and most importantly not trivial javascript challenges?
Answer 1, Authority 100%
Look Quizful – online tests
Tests here. For training at all norms. Check yourself and practicing.
Answer 2, Authority 17%
It is necessary to disassemble all the trivial, since not trivial is a chapacity of several trivial.
Answer 3
For me, it was a problem that there are no resources in Russian.
Found a steep site http://javascript-tasks.ru/
everything in Russian, at different levels of difficulty.