Sequential Promise Processor : First to Resolve, First to Reject : Simple Helper Methods

promise-sequence.js

/**
 * 
 * Inspired by https://www.abeautifulsite.net/executing-promises-in-sequence-and-stopping-at-the-first-resolved-promise
 * 
 * Usage:
 * 
 
 import * as promise_seq from 'promise-sequence';
 
 return new Promise((resolve, reject)=>{
    let ordered_promise_sequence_array = [
      some_ordered_method_which_returns_a_promise,
      another_ordered_method_which_returns_a_promise,
      a_third_ordered_method_which_returns_a_promise
    ];

    promise_seq.first_to_reject(ordered_promise_sequence_array)
      .then(resolve)
      .catch(reject);
      
    // OR
    
    promise_seq.first_to_resolve(ordered_promise_sequence_array)
      .then(resolve)
      .catch(reject);
  });
 
 **/

export const first_to_reject = (seq) => {
  return new Promise(function (resolve, reject) {
    // Any left to process?
    if (seq.length === 0) {
      // All Resolved!
      resolve();
    }
    // Try the first promise in the seq.
    seq[0].call().then(function (val) {
      // Resolved, remove the first item from the array and recursively
      // try the next one
      seq.shift();
      first_to_reject(seq).then(resolve).catch(reject);
    }).catch(function () {
      // Rejected, fail early, skip the rest of the seq. we're all done!
      reject.apply(this, arguments);
    });
  });
}

export const first_to_resolve = (seq) => {
  return new Promise(function (resolve, reject) {
    // Any left to process?
    if (seq.length === 0) {
      // All Rejected!
      reject();
    }
    // Try the first promise in the seq.
    seq[0].call().then(function () {
      // Resolved, we're all done!
      resolve.apply(this, arguments);
    }).catch(function () {
      // Rejected, remove the first item from the array and recursively
      // try the next one
      seq.shift();
      first_to_resolve(seq).then(resolve).catch(reject);
    });
  });
}