I love writing clear and simple code that gets the job done :-). If the Promise that then is called on adopts a state (fulfillment or rejection) for which then has no handler, a new Promise is created with no additional handlers, simply adopting the final state of the original Promise on which then was called. The catch() method returns a Promise and deals with rejected cases only. So unless invoking that function returns a function that returns a Promise, you're not correctly chaining… It's for this purpose that Promise.resolve and Promise.reject exist. If one or both arguments are omitted or are provided non-functions, then then will be missing the handler(s), but will not generate any errors. catch() will swallow errors from non-asynchronous code, which is a very common use case. We hope it makes your life a little bit easier! Built with Love. Promises are an alternative to callbacks for delivering the results of an asynchronous computation. It behaves the same as calling Promise.prototype.then(undefined, onRejected) (in fact, calling obj.catch(onRejected) internally calls obj.then(undefined, onRejected)). The Sails framework is built by a web & mobile shop in Austin, TX, with the help of our contributors.We created Sails in 2012 to assist us on Node.js projects. Michal Charemza I’m a full stack web developer, currently focusing on the front-end using AngularJS in both new and existing web-applications. Photo by Kabun (CC BY NC SA 2.0) “Master the JavaScript Interview” is a series of posts designed to prepare candidates for common questions they are likely to encounter when applying for a …
If you're trying to chain based on the result of a promise, catch() won't behave the way you want.
Handling errors in .catch() also causes problems when you're chaining promises, as .catch always returns a resolved promise. Naturally we open-sourced it. 25.1 Overview #. When you chain promises, you invoke the next function in the chain with the result of the previous function. This means that you have to provide an onRejected function even if you want to fall back to an undefined result value - for example obj.catch(() = {}). However, you're invoking your function that returns a promise directly. Shorthands. However, you're invoking your function that returns a promise directly. So unless invoking that function returns a function that returns a Promise, you're not correctly chaining…
// suppose this list came from localStorage var users = [{id: 1, firstName: "John", lastName: "Doe"}] // in that case, `users` may or may not exist depending on whether there was data in localStorage var promise = users ? They require more effort from implementors of asynchronous functions, but provide several benefits for users of those functions. When you chain promises, you invoke the next function in the chain with the result of the previous function. Sometimes, you already have a value, but want to wrap it in a Promise.
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