p-map - testing concurrency when errors happen

pmap-test.js

const pmap = require('p-map');

const delay = (n) => new Promise(res => setTimeout(res, n));

const promises = [
    new Promise(async (res) => {
        await delay(20);
        res('a')
    }),
    new Promise(async (res) => {
        await delay(10);
        res('b')
    }),
    new Promise(async (res, rej) => {
        await delay(11);
        rej('c')
    }),
    new Promise(async (res, rej) => {
        await delay(19);
        res('d')
    }),
    new Promise(async (res) => {
        await delay(21);
        res('e')
    })
];

process.on('unhandledRejection', error => {
  // Will print "unhandledRejection err is not defined"
  console.log('unhandledRejection', error);
});

result =  []
pmap(promises, x => result.push(x), { concurrency: 2}).then(x => console.log(result));