Nit: Also, I don't like one-line, no-brace things in C-style languages (JSHint would yell at you), but that's just me.

Also, you could skip the return if you just checked if those user ids *weren't* the same and run the code inside that if statement. It's one extra line (assuming you keep the same-line return) and it's more "nested" but I think it reads easier.