Please do not require compiled file. The Emacs Lisp files can be used in non-compiled forms e.g. to reduce space and for debugging purposes.

The compilation step should be a user's choice, not a requirement.

In my experience, users do not byte-compile their files. The mode is some 40x slower when not compiled, which would lead to complaints and support issues.

js2-mode is going into emacs 23.2 soon, after which we can remove the flag because it will be compiled as part of the distribution.