Race all promises once and resolve with the first resolved promise or reject with the last error. Useful for connecting.

raceWithTimeout.js

"use strict"
// race all promises once and resolve with the first resolved promise or reject with the last error.
function raceWithTimeout (promiseList) {
  const TIMEOUT = 50
  return Promise.race([
    ...promiseList.map(suppressReject), // if any resolve, resolve with that result.
    lastRejectionWithTimeout(promiseList, TIMEOUT) // if all reject, reject with last error; if timeout, reject with latest error.
  ])
}

function lastRejectionWithTimeout(promiseList, timeoutMs) {
  return new Promise((_, reject) => {
    let numEndedPromises = 0
    let lastError = null
    setTimeout(() => reject(Object.assign(lastError, {message: `Timed out. Latest error: ${lastError.message}`})), timeoutMs)
    promiseList.forEach(promise => promise
      .then(rejectLastIfPromisesDone)
      .catch(error => {
        lastError = error
        rejectLastIfPromisesDone()
      })
    )
    function rejectLastIfPromisesDone () {
      numEndedPromises = numEndedPromises + 1
      if (numEndedPromises === promiseList.length && lastError) {
        reject(lastError)
      }
    }
  })
}

function suppressReject (promise) {
  return new Promise(resolve => promise.then(resolve))
}

raceWithTimeout([
  new Promise((resolve, reject) => {setTimeout(() => reject(new Error("bad config")), 10)}),
  new Promise((resolve, reject) => {setTimeout(() => reject(new Error("wrong password")), 0)}),
]).then(result => console.log("X", result)).catch(error => console.error(error.message === "bad config" ? "√" : "X", error))

raceWithTimeout([
  new Promise((resolve, reject) => {setTimeout(() => reject(new Error("bad config")), 10)}),
  new Promise((resolve, reject) => {setTimeout(() => resolve("connection"), 20)}),
  new Promise((resolve, reject) => {setTimeout(() => reject(new Error("wrong password")), 0)}),
]).then(result => console.log("√", result)).catch(error => console.error("X", error))

raceWithTimeout([
  new Promise((resolve, reject) => {setTimeout(() => reject(new Error("bad config")), 30)}),
  new Promise((resolve, reject) => {setTimeout(() => reject(new Error("wrong password")), 40)}),
  // timeout at 50
  new Promise((resolve, reject) => {setTimeout(() => resolve("connection"), 60)}),
  new Promise((resolve, reject) => {setTimeout(() => reject(new Error("unknown server")), 70)}),
]).then(result => console.log("√", result)).catch(error => console.error(error.message === "Timed out. Latest error: wrong password" ? "√" : "X", error))