multiret

JavaScript utility library for Promises with multiple return values

Multiple return values simplify complex error handling

Exceptions can make it difficult to determine context and rollback actions when handling multiple asynchronous business operations. Jumping to a catch block without context requires unnecessary boilerplate just to regain that context (for example switch statements against custom codes added in the try block). Instead a mutiple-return promise would be more convenient. Consider this example:

const [docsErr, docs] = await getDocuments();
 
if (docsErr) {
  // propogate the error, can't do anything without docs
}
 
const [imgsErr, imgs] = await getImages(docs);
 
if (imgsErr) {
  // log the error and return the docs
  // (i.e. send a partial result rather than a complete failure)
} else {
  // return the docs and images
}

This paradigm adopts the strengths of the classic error-first signature while fully embracing async/await and promises. try/catch is an excellent companion to async/await and Promise, however it lacks nuance when working with complex transactions. It's more like a hammer when working on a chip board. This library is born of painful personal experience from writing the same patterns and boilerplate over and over again in enterprise services.

Multi-return promises are especially useful for loops where Promise.all would not return the full list of errors. Instead this is possible:

const [errors, results] = await group([
  getPeople(),
  getCompanies(),
])
 
// ... after asserting no errors, destructure to get individual results:
const [people, companies] = results;

Installation

$ npm install multiret

Usage

const multiret = require('multiret');

API

multiret(promise)

Forces a Promise to resolve with a [err, result] signature

multiret.group([...promises])

Forces an array of multi-return promises to resolve with an [errors, results] signature. Similar to Promise.all, except that it does not stop on the first promise rejection

multiret.retry(fn, opts)

Retry an AsyncFunction fn according to opts options.

Options:

interval: number

Initial time to wait in milliseconds.

Default: 1000

factor: number

Exponential growth factor for interval

Default: 2

forever: boolean

Flag to ignore limit and have infinite retries.

Default: false

limit: number

Maximum number of retries.

Default: 10

couldRetry(err, result): function

Test if retry should occur.

Default: () => true

Author

Faraz Syed

License

MIT