| 1. Compiling/building is an ~optional layer on top of the core language/standard (which has become less optional over time) 2. Running JS outside of the browser is similarly a layer that was built before any kind of standard existed for it (which still doesn't, really) The browser standards are the only real standards. Everything else (which has turned into a lot) is "standard by implementation". Implementations usually try to agree with each other, because that's obviously beneficial for everybody, but sometimes they make choices to deviate either out of necessity or in an attempt to improve the ecosystem So it's all pretty ad-hoc, but in practice most things are mostly compatible most of the time. They orbit the same general things, and the orbit has narrowed in the last few years as most of the big problems have been solved and the community is zeroing in on the agreed solutions (with the caveat of often having to maintain legacy compatibility) Deno takes a stricter philosophy than most, where it prescribes a ~good way that everything should be done (which is almost entirely based on browser standards which have evolved since all this started), even though it runs outside of a browser, and requiring the ecosystem to fall in line Bun on the other hand takes a maximalist approach to compatibility; it does its best to make everything from every other sub-ecosystem Just Work without any modifications |