Not for purists, but then this wasn't made for purists, never mind that purists would unlikely use JS at all. Not a con. It opens up JS coding to anyone. Couldn't fit this in the Pros. This is Education by the hand. Well done!
Until better languages compiled to web-assembly appear it gets a set of proven educational techniques right. Live feedback, fun, exercises.
Suggestion for next iteration: core, minimal, high level //comments in plain english, to offer a leg up in key OOP concepts. 5th tab maybe.
waiting for new levels
отличный способ научиться js
no function «skip level»
would be good a live tutorial like "click here" and "then here"
Simple / Helpful
maybe automatic execution of code and keyboard shortcuts