What you describe is the "old" way to use promises.

Instead, you can yield promises inside generator functions, or better yet use async/await with a transpiler. Both methods give you nice sync-looking code.

Good to know!

> something which is contagious

I guess what you're trying to say is that once you adopt Promises a large portion of your code will have to be tailored to use it.

To which I respond: .. yes, so what? It's better than callbacks. And it's better than some "magic fairydust" that doesn't make it explicit that you're doing something async.

Promises are better than callbacks but far worse (in terms of complexity they create) that synchronous code. This might be fairy dust but it crushes promises for reducing developer cognitive load. Having said that I agree with the person who commented that async/await is a better way to go (although sadly not really an option in CS yet).

Why would someone invest in Coffeescript at this point with ES6 + Babel being a highly viable option?

Sorry could you explain what CS is? I can't think of anything besides computer science.

CoffeeScript! :-) One of those neat compiles-to-JS languages!

Edit: And the "problem" with async/await and CoffeeScript is that the former is currently available in various JS transpilers but you can't use one of those and CoffeeScript at the same time.

> once you adopt Promises a large portion of your code will have to be tailored to use it.

This isn't a necessity, since you can create a function which both returns a Promise and accepts a callback. Most Promise libraries make this easy to support, which makes it easy to introduce Promises into projects that already use callbacks, and vice-versa.

Definitely better than callbacks, but debatable wether this solution or promises is better. I like both.