for (let i = 0; i < 10; i++) { const promise = new Promise((resolve, reject) => { const timeout = Math.random() * 1000; setTimeout(() => { console.log(i); }, timeout); }); // TODO: Chain this promise to the previous one (maybe without having it running?) } The above will give the following random output: 6 … Read more
I have a pure JavaScript Promise (built-in implementation or poly-fill): var promise = new Promise(function (resolve, reject) { /* … */ }); From the specification, a Promise can be one of: ‘settled’ and ‘resolved’ ‘settled’ and ‘rejected’ ‘pending’ I have a use case where I wish to interrogate the Promise synchronously and determine: is the … Read more
I would like to clarify this point, as the documentation is not too clear about it; Q1: Is Promise.all(iterable) processing all promises sequentially or in parallel? Or, more specifically, is it the equivalent of running chained promises like p1.then(p2).then(p3).then(p4).then(p5)…. or is it some other kind of algorithm where all p1, p2, p3, p4, p5, etc. … Read more
Looking at MDN it looks like the values passed to the then() callback of Promise.all contains the values in the order of the promises. For example: var somePromises = [1, 2, 3, 4, 5].map(Promise.resolve); return Promise.all(somePromises).then(function(results) { console.log(results) // is [1, 2, 3, 4, 5] the guaranteed result? }); Can anybody quote a spec stating … Read more
I’m building a frontend app with React and Redux and I’m using axios to perform my requests. I would like to get access to all the fields in the header of the response. In my browser I can inspect the header and I can see that all the fields that I need are present(such as … Read more
For learning Angular 2, I am trying their tutorial. I am getting an error like this: (node:4796) UnhandledPromiseRejectionWarning: Unhandled promise rejection (r ejection id: 1): Error: spawn cmd ENOENT [1] (node:4796) DeprecationWarning: Unhandled promise rejections are deprecated. In the future, promise rejections that are not handled will terminate the Node. js process with a non-zero … Read more
Suppose I have the following code. function divide(numerator, denominator) { return new Promise((resolve, reject) => { if(denominator === 0){ reject(“Cannot divide by 0”); return; //superfluous? } resolve(numerator / denominator); }); } If my aim is to use reject to exit early, should I get into the habit of returning immediately afterward as well? 6 Answers … Read more
How can I reject a promise that returned by an async/await function? e.g. Originally: foo(id: string): Promise<A> { return new Promise((resolve, reject) => { someAsyncPromise().then((value)=>resolve(200)).catch((err)=>reject(400)) }); } Translate into async/await: async foo(id: string): Promise<A> { try{ await someAsyncPromise(); return 200; } catch(error) {//here goes if someAsyncPromise() rejected} return 400; //this will result in a resolved … Read more
I have been using ES6 Promise. Ordinarily, a Promise is constructed and used like this new Promise(function(resolve, reject){ if (someCondition){ resolve(); } else { reject(); } }); But I have been doing something like below to take the resolve outside for the sake of flexibility. var outsideResolve; var outsideReject; new Promise(function(resolve, reject) { outsideResolve = … Read more
Whether it’s an ES6 Promise or a bluebird Promise, Q Promise, etc. How do I test to see if a given object is a Promise? 19 Answers 19
