It is considered a good practice to embed the whole function body inside the Promise constructor, so should any error happen, it would be converted to a rejection. In this case it solves your problem too I believe. saveMyClass(updatedMyClass: MyClass) { return new Promise<Package>((resolve, reject) => { //saving MyClass using http service //return the saved … Read more
You can attach a then handler that sets a done flag on the promise (or the RunTest instance if you prefer), and test that: if (!this.promise) { this.promise = this.someTest(); this.promise.catch(() => {}).then(() => { this.promise.done = true; }); retVal = true; } if ( this.promise.done ) { this.promise = this.someTest(); this.promise.catch(() => {}).then(() => … Read more
The whole world is waiting for the unhandledrejection and rejectionhandled events. As of March 2016, Chrome is now the first to support it. Example: window.addEventListener(‘unhandledrejection’, function(event) { console.error(‘Unhandled rejection (promise: ‘, event.promise, ‘, reason: ‘, event.reason, ‘).’); }); Specification: HTML Living Standard Mozilla Developer: onrejectionhandled, onunhandledrejection Chromium Issues: 495801, 393913
Fetch returns a promise, and you can chain multiple promises, and use the result of the 1st request in the 2nd request, and so on. This example uses the SpaceX API to get the info of the latest launch, find the rocket’s id, and fetch the rocket’s info. const url=”https://api.spacexdata.com/v4″; const result = fetch(`${url}/launches/latest`, { … Read more
What happens with a Promise Same thing with a function that returns void. A void function returns undefined. A Promise<void> resolves to an undefined. function foo(){}; console.log(foo()); // undefined async function bar(){}; bar().then(res => console.log(res)); // undefined
Putting the unhandledRejection inside a middleware…often results in a Error: Can’t render headers after they are sent to the client. Make a slight change to your error handler: // production error handler const HTTP_SERVER_ERROR = 500; app.use(function(err, req, res, next) { if (res.headersSent) { return next(err); } return res.status(err.status || HTTP_SERVER_ERROR).render(‘500’); }); From the ExpressJS … Read more
This happens because you do not attach a catch handler to the promise returned by the first then method, which therefore is without handler for when the promise rejects. You do have one for the promise p in the last line, but not for the chained promise, returned by the then method, in the line … Read more
// This does not work, since the Promise returned by `json()` is never fulfilled return Promise.reject(resp.json()); Well, the resp.json promise will be fulfilled, only Promise.reject doesn’t wait for it and immediately rejects with a promise. I’ll assume that you rather want to do the following: fetch(url).then((resp) => { let json = resp.json(); // there’s always … Read more
The problem is that when it rejects, it doesn’t go to my error middleware, but if I remove the async keyword and throw inside a middleware it does. express doesn’t support promises currently, support may come in the future release of express@5.x.x So when you pass a middleware function, express will call it inside a … Read more
What’s the stuff inside [[]] My question is what do the double brackets [[ ]] mean, and how do I retrieve the value of [[PromiseValue]]. It’s an internal property. You cannot access it directly. Native promises may only be unwrapped in then with promises or asynchronously in generally – see How to return the response … Read more