There is actually an immediate real world use for this (not just being a toy): online judge (like leetcode). Of course, the final evaluation has to be done on t

There is actually an immediate real world use for this (not just being a toy): online judge (like leetcode). Of course, the final evaluation has to be done on the server to avoid cheating on the test set, but the user can do his/her own test in the browser without the roundtrip to and from the server then.