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.

Related

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