I have no clue what these people were talking about. Unwieldy how? What kind of conflicts? CoffeeScript is totally compatible with JavaScript — in fact, it bends over so far backwards to be compatible with JavaScript that it falls way short of its potential. This all sounds like FUD from some antihipster who just likes to hate on new things. (Which is not to say he or she isn't a smart person overall — everybody has some area where they're irrational.)