Update, you probably want to use the built-in native Promise.allSettled: Promise.allSettled([promise]).then(([result]) => { //reach here regardless // {status: “fulfilled”, value: 33} }); As a fun fact, this answer below was prior art in adding that method to the language :] Sure, you just need a reflect: const reflect = p => p.then(v => ({v, status: … Read more
There is no advantage of using one vs the other, but, there is a specific case where throw won’t work. However, those cases can be fixed. Any time you are inside of a promise callback, you can use throw. However, if you’re in any other asynchronous callback, you must use reject. For example, this won’t … Read more
The deferred antipattern (now explicit-construction anti-pattern) coined by Esailija is a common anti-pattern people who are new to promises make, I’ve made it myself when I first used promises. The problem with the above code is that is fails to utilize the fact that promises chain. Promises can chain with .then and you can return … Read more
Break the chain When you need to access the intermediate values in your chain, you should split your chain apart in those single pieces that you need. Instead of attaching one callback and somehow trying to use its parameter multiple times, attach multiple callbacks to the same promise – wherever you need the result value. … Read more
Async arrow functions look like this: const foo = async () => { // do something } Async arrow functions look like this for a single argument passed to it: const foo = async evt => { // do something with evt } Async arrow functions look like this for multiple arguments passed to it: … Read more
Promises have state, they start as pending and can settle to: fulfilled meaning that the computation completed successfully. rejected meaning that the computation failed. Promise returning functions should never throw, they should return rejections instead. Throwing from a promise returning function will force you to use both a } catch { and a .catch. People … Read more
Promise A Promise handles a single event when an async operation completes or fails. Note: There are Promise libraries out there that support cancellation, but ES6 Promise doesn’t so far. Observable An Observable is like a Stream (in many languages) and allows to pass zero or more events where the callback is called for each … Read more
Sure the code does work, but I’m pretty sure it doesn’t do what you expect it to do. It just fires off multiple asynchronous calls, but the printFiles function does immediately return after that. Reading in sequence If you want to read the files in sequence, you cannot use forEach indeed. Just use a modern … Read more