P-reflect NPM | npm.io

p-reflect

Make a promise always fulfill with its actual fulfillment value or rejection reason

Useful when you want a promise to fulfill no matter what and would rather handle the actual state afterwards.

Install

$ npm install p-reflect

Usage

Here, Promise.all would normally fail early because one of the promises rejects, but by using p-reflect, we can ignore the rejection and handle it later on.

import pReflect from 'p-reflect';

const promises = [
	getPromise(),
	getPromiseThatRejects(),
	getPromise()
];

const results = await Promise.all(promises.map(pReflect));

console.log(results);
/*
[
	{
		status: 'fulfilled',
		value: '🦄'
		isFulfilled: true,
		isRejected: false
	},
	{
		status: 'rejected',
		reason: [Error: 👹]
		isFulfilled: false,
		isRejected: true
	},
	{
		status: 'fulfilled',
		value: '🐴'
		isFulfilled: true,
		isRejected: false
	}
]
*/

const resolvedString = results
	.filter(result => result.isFulfilled)
	.map(result => result.value)
	.join('');

console.log(resolvedString);
//=> '🦄🐴'

The above is just an example. Use p-settle if you need exactly that.

API

pReflect(promise)

Returns a Promise<Object>.

The object has the following properties:

status ('fulfilled' or 'rejected', depending on how the promise resolved)
value or reason (Depending on whether the promise fulfilled or rejected)
isFulfilled
isRejected

promise

Type: Promise

A promise to reflect upon.

isFulfilled(object)

This is a type guard for TypeScript users.

Returns true if the object has the property value, false otherwise.

This is useful since await pReflect(promise) always returns a PromiseResult. This function can be used to determine whether PromiseResult is PromiseFulfilledResult or PromiseRejectedResult.

This is a workaround for microsoft/TypeScript#32399

reference documentation Using type predicates

isRejected(object)

This is a type guard for TypeScript users.

Returns true if the object has the property reason, false otherwise.

This is useful since await pReflect(promise) always returns a PromiseResult. This function can be used to determine whether PromiseResult is PromiseRejectedResult or PromiseFulfilledResult.