defer reject

Defer rejection explicitly until a catch handler is attached.

Install

$ npm i defer-reject

Usage

import { deferReject } from 'defer-reject';

async function work1()
{
    await new Promise((_resolve, reject) => {
        setTimeout(() => {
            reject(new Error('rejected'))
        }, 1000)
    });
}

async function work2()
{
    return new Promise(resolve => setTimeout(resolve, 2000));
}

async function work()
{
    try{
        const work1_result = deferReject(work1());
        await work2();
        return await work1_result;
    }catch(e){
        console.log("Caught:", e);
    }
}

work();

API

deferReject<T>(promise: Promise<T>): Promise<T>: defer rejection of a promise until a catch handler is attached(awaited or catch(onrejected) or then(onfulfilled, onrejected) is called).

RejectDeferredPromise<T>: a promise with deferred rejection. constructor is same as Promise<T>

W?

After node v15.0.0, unhandled rejections will emit unhandledRejection events by default. If an unhandledRejection event is not handled, it will throw an error and exit the process.

try {
    // if this rejects before work2 is finished, the process will exit
    const p1: Promise<T> = work1();

    await work2();
    return await p1;
}
...

With the deferReject() function, rejection will be deferred until the promise is awaited or catch(onrejected) or then(onfulfilled, onrejected) is called. This will prevent the process from exiting without changing --unhandled-rejections.

try {
    // exception will be caught by catch block
    const p1: Promise<T> = deferReject(work1());

    await work2();
    return await p1;
}
...