[].slice will create new object and Array.prototype.slice don't

Fair points, but it shouldn't be marked as "incorrect" since the requirements you've listed are not mentioned in the description.

In general, I agree: Keep the braces on the same line as the control statement. However, the auto semicolon insertion feature does not impact everything everywhere. The style here in zaider's code is to drop the brace for functions only. This style is perfectly safe, and as long as one doesn't stray and become over zealous and begin to drop more braces, everything will work just fine.