Awesome

awesome-imperative-promise

Offer an imperative API on top of promise, with cancellation support

Install

npm install --save awesome-imperative-promise
// or
yarn add awesome-imperative-promise

Features

• Imperative methods to trigger promise resolve/reject
• Imperative method to trigger promise cancellation (the promise will never resolve/reject)
• Can wrap an existing promise or simply create a new one
• Typescript native support

Usage

import { createImperativePromise } from "awesome-imperative-promise";

const wrappedPromise = fetch("url");

// Wrap an existing promise and expose some additional imperative methods
// The existingPromise paramter is optional and the returned promise with resolve/reject when the existing promise do
const { promise, resolve, reject, cancel } = createImperativePromise(wrappedPromise);

// will make the returned promise resolved (not the wrapped one)
resolve("some value");

// will make the returned promise reject (not the wrapped one)
reject(new Error(":s"));

// will ensure the returned promise never resolves or reject
cancel();

Important note:

The returned promise can only resolve/reject/cancel once and will ignore further imperative calls like regular promises do. If you call cancel() and then call resolve("val") (or if the wrapped promise resolves), the returned promise will never resolve because it has been cancelled first.

Why

I find this useful to be able to cancel the resolution of promises, and use this lib as an implementation detail in other libs I build, like awesome-debounce-promise.

This is particularly useful in React apps where you want to ensure an async process is cancelled when component unmounts, to avoid triggering a setState and get a warning. See [isMounted() is an antipattern] (https://reactjs.org/blog/2015/12/16/ismounted-antipattern.html)

License

MIT © slorber

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