My understanding is that is the problem repl.it is trying to solve. In a sentence: think about your code and not your environment.
My curmudgeonly self thinks that there are deeper problems and externalities that programming on a phone/tablet or in the web only exasperate. Computer literacy is shockingly poor among the incoming generation of people who have only used mobile devices, WebUIs, and maybe a Chromebook - and that's not the fault of people or technology, but the business models that only succeed by locking users into platforms and hiding details of how those platforms work. The issue with programming on mobile or through something like repl.it is that it hides too much - at the end of the day, tinkering with computers requires computers that can be tinkered with and software systems that can be introspected.