[JavaScript] to promise or to callback? This is the problem

Hmm. If every library author took the second approach there would be tons of wasted code. This may not be a bad thing but it bothers my OCD.<p>It would be nice if you could write callback-only or promise-only code and have a post-processor produce two .JS files. One with callbacks and one with promises. Then somehow, just as magically, you could require either one. This would save memory and my OCD.