Shortly, the order is preserved. Following the spec you linked to, Promise.all(iterable) takes an iterable as a parameter and internally calls PerformPromiseAll(iterator, constructor, resultCapability) with it, where the latter loops over iterable using IteratorStep(iterator). Resolving is implemented via Promise.all() Resolve where each resolved promise has an internal [[Index]] slot, which marks the index of the … Read more
Update (2017) Here in 2017, Promises are built into JavaScript, they were added by the ES2015 spec (polyfills are available for outdated environments like IE8-IE11). The syntax they went with uses a callback you pass into the Promise constructor (the Promise executor) which receives the functions for resolving/rejecting the promise as arguments. First, since async … Read more
Update: jQuery 3.0 has fixed the problems outlined below. It is truly Promises/A+ compliant. Yes, jQuery promises have serious and inherent problems. That said, since the article was written jQuery made significant efforts to be more Promises/Aplus complaint and they now have a .then method that chains. So even in jQuery returnsPromise().then(a).then(b) for promise returning … Read more
One go-around of the event loop will have exactly one task being processed from the macrotask queue (this queue is simply called the task queue in the WHATWG specification). After this macrotask has finished, all available microtasks will be processed, namely within the same go-around cycle. While these microtasks are processed, they can queue even … Read more
This feature was added to the 1.1.5 release via a timeout parameter: var canceler = $q.defer(); $http.get(‘/someUrl’, {timeout: canceler.promise}).success(successCallback); // later… canceler.resolve(); // Aborts the $http request if it isn’t finished.
Here are some simple examples for how you sequence through an array executing each async operation serially (one after the other). Let’s suppose you have an array of items: var arr = […]; And, you want to carry out a specific async operation on each item in the array, one at a time serially such … Read more
Let’s start with the general rule for using promises: Every function that does something asynchronous must return a promise Which functions are these in your case? It’s getPrayerInCat, the forEach callback, and Prayer.find. Hm, Prayer.find doesn’t return a promise, and it’s a library function so we cannot modify it. Rule 2 comes into play: Create … Read more
Every async function returns a Promise object. The await statement operates on a Promise, waiting until the Promise resolves or rejects. So no, you can’t do console.log on the result of an async function directly, even if you use await. Using await will make your function wait and then return a Promise which resolves immediately, … Read more
Yes, you can do that, and it will run the two asynchronous functions in parallel. You’ve just created a promise and thrown it away. However, this means that when the promise is rejected you won’t notice. You’ll just get an unhandledRejection eventually which will crash your process if not handled. Is this OK? How can … Read more
The callbacks attached to done() will be fired when the deferred is resolved. The callbacks attached to fail() will be fired when the deferred is rejected. Prior to jQuery 1.8, then() was just syntactic sugar: promise.then( doneCallback, failCallback ) // was equivalent to promise.done( doneCallback ).fail( failCallback ) As of 1.8, then() is an alias … Read more