Most developers would agree that, all other things being equal, a synchronous program is easier to work with than an asynchronous one. The logic for this is pretty clear: one flow of execution is easier for the human mind to simulate than n
concurrent flows.
After doing two small projects in node.js (one of which is here -- ready for the blinding flurry of criticism), there's one question that I can't shake: if asynchronicity is an optimization (that is, a complexity introduced for the sake of performance), why would people, a priori, turn to a framework that imposes it for everything? If asynchronous code is harder to reason about, why would we elect to live in a world where it is the default?
It could be argued pretty well that the browser is a domain that inherently lends itself to an async model, but I'd be very curious to hear a defense of "async-first" thinking for problems that are typically solved on the server-side. When working with node, I've noticed many regions of code where
- synchronicity wouldn't introduce a performance bottleneck, and
- what would otherwise be an easy problem is made very difficult by the fact that everything must be phrased for the event loop.
For an example of this, try writing a function call that requires information from two separate HTTP API responses; I basically need to draw a diagram of what happens with async.waterfall
for a task that, given synchronicity, would've been solved with a trivial three-liner.
Easy things should be easy. Optimizations should be closeted until they're needed. Maybe I'm missing something here, some mechanism in node that allows opt-in synchronicity... dear node.js, is there such a thing? If not, why do you want to make many things harder than they need to be?
IMHO, the main problem with promises is that people only use them half-way. Properly leveraged, all the async goes away and it looks exactly like sync code written in ruby or whatever, but automatically optimized to run async behind the scenes.
People keep missing that point and writing "then" all over their code, turning "callback-hell" into "then-hell".
I gave a presentation on this topic recently: https://speakerdeck.com/jakobmattsson/how-to-star-actually-star-use-promises-in-javascript. Jump right to slide 40 if you want to see what promises should look like. Compare with the 4 pages preceding it.
The lib referred to can be found here: https://github.com/jakobmattsson/z-core