And what happens when the keys aren't a or b , you really should try to make it generic :)

print is ok, i think join is recursion, i used 'while do end', passed, thank u!

Maybe you try to print the resulting list and it is printed recursively?

i used ruby and used join Method, is join recursion?

I guess you use recursion and it results in too deep stack level. You likely need to rewrite your code in non-recursive manner as JS doesn't have tail-call optimization.

SystemStackError: stack level too deep, how can i fix it?

Same here too

how can i write test?? Test.assert_equals( list([ {name: 'Bart'} ]), 'Bart') or Test.assert_equals( list([ {name: 'Bart'} ]), "should return 'Bart'"). Thank u very much!

pass, but not best, ought to use sort_by