var fn = async (param) => new Promise((res, rej) => {
...
fooLibraryCall(param).then(res).catch(rej);
});
I've literally seen similar to this... where devs see wrappers for the callback syntax, then apply the same to thenables and use manual Promises inside an async labelled function. It makes my mind bleed to see it, and I've seen it a few places.Then, of course, there's dealing with module imports and async import() methods and how they operate or get transpiled or split, etc.
Sometimes I'll add a `.catch(() => null)` or similar for manipulating a specific call with `.then`, if I want to manipulate something out of flow. Such as a convenience method to normalize api fetch calls, etc. That's just useful functionality, not making literally wrappers for no benefit or reason.
But all of them? Over a given program’s lifetime? In aggregate these end up being responsible for an absolutely wild number of random bugs that crop up in your exception logs that need to get tracked down. And it never ends. There are an infinite number of edge cases you’ve never thought about that aren’t fully handled and that some of which are constantly being tripped.
This just… doesn’t happen in Rust. The type system catches (and/or completely rules out) a ridiculous number of these situations. I have repeatedly written finished software in Rust, where once it was released there was only an occasional need to add features but the typical bug-squashing treadmill just doesn’t exist.
That’s not to say there are never bugs. You can express faulty logic in any language. But the number of stupid impedance matches that are categorically ruled out makes the experience of operating and maintaining Rust program once written a widely different experience than I’ve had with any other language.
The 'difficulty' of Rust would have been preferable, in hindsight.
As others have noted, the JavaScript program has a bug not present in the Rust program, and a syntax error (should probably use for..of, not for..in). The example definitely uses more concepts than "first-class functions". You still have to understand iterators, just like in Rust, and it uses CommonJS instead of ES Modules, but I digress. The usage of async/await and Promises is another concept to teach, and the usage of top-level await is specifically something that wasn't supported in some runtimes (e.g. Node) until recently. It still isn't supported in the latest version of some mainstream JS engines (e.g. Hermes, which is used in React Native)