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.

1import pReflect from 'p-reflect';
2
3const promises = [
4	getPromise(),
5	getPromiseThatRejects(),
6	getPromise()
7];
8
9const results = await Promise.all(promises.map(pReflect));
10
11console.log(results);
12/*
13[
14	{
15		status: 'fulfilled',
16		value: '🦄'
17		isFulfilled: true,
18		isRejected: false
19	},
20	{
21		status: 'rejected',
22		reason: [Error: 👹]
23		isFulfilled: false,
24		isRejected: true
25	},
26	{
27		status: 'fulfilled',
28		value: '🐴'
29		isFulfilled: true,
30		isRejected: false
31	}
32]
33*/
34
35const resolvedString = results
36	.filter(result => result.isFulfilled)
37	.map(result => result.value)
38	.join('');
39
40console.log(resolvedString);
41//=> '🦄🐴'

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.

Related

• p-settle - Settle promises concurrently and get their fulfillment value or rejection reason
• More…