private handleError(error: any) { // previously // return Observable.throw(‘Some error information’); // now return throwError(‘Some error information’); } See also How to catch exception correctly from http.request()?
In this line stream.on(“end”, resolve(stream.dests[0].path)); you are executing resolve immediately, and the result of calling resolve (which will be undefined, because that’s what resolve returns) is used as the argument to stream.on – not what you want at all, right. .on‘s second argument needs to be a function, rather than the result of calling a … Read more
You can promisify this.setState so that you can use the React API as a promise. This is how I got it to work: class LyricsGrid extends Component { setAsyncState = (newState) => new Promise((resolve) => this.setState(newState, resolve)); Later, I call this.setAsyncState using the standard Promise API: this.setAsyncState({ lyricsCorpus, matrix, count }) .then(foo1) .then(foo2) .catch(err => … Read more
After the initial fetch() call, only the headers have been read. So, to parse the body as JSON, first the body data has to be read from the incoming stream. And, since reading from the TCP stream is asynchronous, the .json() operation ends up asynchronous. Note: the actual parsing of the JSON itself is not … Read more
Async prefix is a kind of wrapper for Promises. async function latestTime() { const bl = await web3.eth.getBlock(‘latest’); console.log(bl.timestamp); // Returns a primitive console.log(typeof bl.timestamp.then == ‘function’); //Returns false – not a promise return bl.timestamp; } Is the same as function latestTime() { return new Promise(function(resolve,success){ const bl = web3.eth.getBlock(‘latest’); bl.then(function(result){ console.log(result.timestamp); // Returns a … Read more
C# solves this with Tasks Tasks solve the same problem as promises do in JavaScript – and you can use them similarly. However normally, you shouldn’t. There are several differences: Tasks have cancellation built in. Tasks aren’t always started, and you can have tasks and start them later. Promises perform assimilation, you can’t have a … Read more
My closest guess … it keeps track of the active things happening in your code, when there is nothing else happening, it simply exits. This is essentially correct. Node keeps a reference count of things like timers and network requests. When you make a network, or other async request, set a timer, etc. Node adds … Read more
ES2015 promises will never have progression. Promises represent a singular eventual value. If you want multiple values you can look into observables – or put the progress on the promise returning function. Putting the progress on the promise returning function is pretty easy. Basically you take a callback as a parameter to the function and … Read more
Logging the error object won’t print error’s stack trace. You need to ask for it specifically: console.error(‘You had an error: ‘, err.stack);
Edit 2021 all platforms have converged on AbortController as the cancellation primitive and there is some built in support for this. In Node.js // import { setTimeout } from ‘timers/promises’ // in ESM const { setTimeout } = require(‘timers/promises’); const ac = new AbortController(); // cancellable timeout (async () => { await setTimeout(1000, null, { … Read more