implementations of looping with Bluebird promises

promiseForEach.js

// promisey foreach loop

'use strict';

var Promise = require('bluebird'),
    promiseWhile = require('./promiseWhile');

/**
 * Promisey foreach
 *
 * @param {Array} arr
 * @param {Function} action which acts on element of arr, returns Promise
 * @param {Function} errorHandler see promiseWhile
 * @return {Promise}
 */
function promiseForEach(arr, action, errorHandler) {
  var i = 0;

  var condition = function() {
    return i < arr.length;
  };

  var actionIterator = Promise.method(function() {
    var val = arr[i];
    i++;
    return action(val);
  });

  return promiseWhile(condition, actionIterator, errorHandler);
}


module.exports = promiseForEach;

promiseWhile.js

// promisey while loop with promisey conditionals
// (so, your condition can potentially do I/O)

'use strict';

var Promise = require('bluebird');

/**
 * Promisey while
 * @param {Function} condition function returning boolean, or function generating a similar Promise
 * @param {Function} action function which takes no args, returns promise
 * @param {Function} errorHandler optional - capture errors during looping, return if should continue iterating. Default to terminate
 * @return {Promise}
 */
function promiseWhile(condition, action, errorHandler) {

  // default errorhandler terminates on first error
  if (typeof errorHandler === 'undefined') {
    errorHandler = function() { console.log("errorHandler"); return false; };
  }

  var promiseCondition;
  if (Promise.is(condition)) {
    promiseCondition = condition;
  } else {
    promiseCondition = Promise.method(condition);
  }
  
  return new Promise(function(resolve, reject) {

    var loop = function() {
      return promiseCondition().then(function(shouldContinue) {
        if (!shouldContinue) {
          return resolve();
        } else {
          return action().then(loop).catch(function() {
            if (errorHandler.apply(this, arguments)) {
              return loop();
            } else {
              return reject();
            }
          });
        }
      });
    };

    // first time
    process.nextTick(loop);

  });
}

module.exports = promiseWhile;