Handling mixed success/fail promises

promise-success-fail-all.js

/**
 * You have 2 promises either of which may fail or succed.
 *
 * You want to run a handler after all have failed or succeeded and have access to the result of each promise.
 *
 * How?
 */
const Promise = require('bluebird');

var fail = n => new Promise((resolve, reject) => setTimeout(function() { reject('fail!') }, n*100));
var pass = n => new Promise((resolve, reject) => setTimeout(function() { resolve('pass!') }, n*100));

// .all() fires the catch() if one fails
Promise.all([fail(1), pass(1)])
  .then(results => console.log('1. all(fail, pass).then:', results))
  .catch(results => console.log('1. all(fail, pass).catch:', results));


// .any() fires the then() if one succeeds, but you won't see the results of the failure
Promise.any([fail(2), pass(2)])
  .then(results => console.log('2. any(fail, pass).then:', results))
  .catch(results => console.log('2. any(fail, pass).catch:', results));

// .any() with 2 failures fires the catch, as nothing succeeded
Promise.any([fail(3), fail(3)])
  .then(results => console.log('3. any(fail, fail).then:', results))
  .catch(results => console.log('3. any(fail, fail).catch:', results));

// .finally() always fires, but doesn't have access to any data
Promise.all([fail(4), pass(4)])
  .catch(error => {})
  .finally(results => console.log('4. all(fail, pass).finally:', results));

// Answer 1:
// Add a .catch() to all - you'll need to deal with undefined values
Promise.all([fail(5), pass(5)].map(p => p.catch(() => new Error('fail!'))))
  .then(results => console.log('5. all(fail.catch(), pass.catch()).then:', results));