neo-async/async.js

Neo-Async is a drop-in replacement for Async, it almost fully covers its functionality and runs faster

(function(global, factory) {
  /*jshint -W030 */
  'use strict';
  typeof exports === 'object' && typeof module !== 'undefined'
    ? factory(exports)
    : typeof define === 'function' && define.amd
    ? define(['exports'], factory)
    : global.async
    ? factory((global.neo_async = global.neo_async || {}))
    : factory((global.async = global.async || {}));
})(this, function(exports) {
  'use strict';

  var noop = function noop() {};
  var throwError = function throwError() {
    throw new Error('Callback was already called.');
  };

  var DEFAULT_TIMES = 5;
  var DEFAULT_INTERVAL = 0;

  var obj = 'object';
  var func = 'function';
  var isArray = Array.isArray;
  var nativeKeys = Object.keys;
  var nativePush = Array.prototype.push;
  var iteratorSymbol = typeof Symbol === func && Symbol.iterator;

  var nextTick, asyncNextTick, asyncSetImmediate;
  createImmediate();

  /**
   * @memberof async
   * @namespace each
   * @param {Array|Object} collection
   * @param {Function} iterator
   * @param {Function} callback
   * @example
   *
   * // array
   * var order = [];
   * var array = [1, 3, 2];
   * var iterator = function(num, done) {
   *   setTimeout(function() {
   *     order.push(num);
   *     done();
   *   }, num * 10);
   * };
   * async.each(array, iterator, function(err, res) {
   *   console.log(res); // undefined
   *   console.log(order); // [1, 2, 3]
   * });
   *
   * @example
   *
   * // array with index
   * var order = [];
   * var array = [1, 3, 2];
   * var iterator = function(num, index, done) {
   *   setTimeout(function() {
   *     order.push([num, index]);
   *     done();
   *   }, num * 10);
   * };
   * async.each(array, iterator, function(err, res) {
   *   console.log(res); // undefined
   *   console.log(order); // [[1, 0], [2, 2], [3, 1]]
   * });
   *
   * @example
   *
   * // object
   * var order = [];
   * var object = { a: 1, b: 3, c: 2 };
   * var iterator = function(num, done) {
   *   setTimeout(function() {
   *     order.push(num);
   *     done();
   *   }, num * 10);
   * };
   * async.each(object, iterator, function(err, res) {
   *   console.log(res); // undefined
   *   console.log(order); // [1, 2, 3]
   * });
   *
   * @example
   *
   * // object with key
   * var order = [];
   * var object = { a: 1, b: 3, c: 2 };
   * var iterator = function(num, key, done) {
   *   setTimeout(function() {
   *     order.push([num, key]);
   *     done();
   *   }, num * 10);
   * };
   * async.each(object, iterator, function(err, res) {
   *   console.log(res); // undefined
   *   console.log(order); // [[1, 'a'], [2, 'c'], [3, 'b']]
   * });
   *
   * @example
   *
   * // break
   * var order = [];
   * var array = [1, 3, 2];
   * var iterator = function(num, done) {
   *   setTimeout(function() {
   *     order.push(num);
   *     done(null, num !== 2);
   *   }, num * 10);
   * };
   * async.each(array, iterator, function(err, res) {
   *   console.log(res); // undefined
   *   console.log(order); // [1, 2]
   * });
   *
   */
  var each = createEach(arrayEach, baseEach, symbolEach);

  /**
   * @memberof async
   * @namespace map
   * @param {Array|Object} collection
   * @param {Function} iterator
   * @param {Function} callback
   * @example
   *
   * // array
   * var order = [];
   * var array = [1, 3, 2];
   * var iterator = function(num, done) {
   *   setTimeout(function() {
   *     order.push(num);
   *     done(null, num);
   *   }, num * 10);
   * };
   * async.map(array, iterator, function(err, res) {
   *   console.log(res); // [1, 3, 2];
   *   console.log(order); // [1, 2, 3]
   * });
   *
   * @example
   *
   * // array with index
   * var order = [];
   * var array = [1, 3, 2];
   * var iterator = function(num, index, done) {
   *   setTimeout(function() {
   *     order.push([num, index]);
   *     done(null, num);
   *   }, num * 10);
   * };
   * async.map(array, iterator, function(err, res) {
   *   console.log(res); // [1, 3, 2]
   *   console.log(order); // [[1, 0], [2, 2], [3, 1]]
   * });
   *
   * @example
   *
   * // object
   * var order = [];
   * var object = { a: 1, b: 3, c: 2 };
   * var iterator = function(num, done) {
   *   setTimeout(function() {
   *     order.push(num);
   *     done(null, num);
   *   }, num * 10);
   * };
   * async.map(object, iterator, function(err, res) {
   *   console.log(res); // [1, 3, 2]
   *   console.log(order); // [1, 2, 3]
   * });
   *
   * @example
   *
   * // object with key
   * var order = [];
   * var object = { a: 1, b: 3, c: 2 };
   * var iterator = function(num, key, done) {
   *   setTimeout(function() {
   *     order.push([num, key]);
   *     done(null, num);
   *   }, num * 10);
   * };
   * async.map(object, iterator, function(err, res) {
   *   console.log(res); // [1, 3, 2]
   *   console.log(order); // [[1, 'a'], [2, 'c'], [3, 'b']]
   * });
   *
   */
  var map = createMap(arrayEachIndex, baseEachIndex, symbolEachIndex, true);

  /**
   * @memberof async
   * @namespace mapValues
   * @param {Array|Object} collection
   * @param {Function} iterator
   * @param {Function} callback
   * @example
   *
   * // array
   * var order = [];
   * var array = [1, 3, 2];
   * var iterator = function(num, done) {
   *   setTimeout(function() {
   *     order.push(num);
   *     done(null, num);
   *   }, num * 10);
   * };
   * async.mapValues(array, iterator, function(err, res) {
   *   console.log(res); // { '0': 1, '1': 3, '2': 2 }
   *   console.log(order); // [1, 2, 3]
   * });
   *
   * @example
   *
   * // array with index
   * var order = [];
   * var array = [1, 3, 2];
   * var iterator = function(num, index, done) {
   *   setTimeout(function() {
   *     order.push([num, index]);
   *     done(null, num);
   *   }, num * 10);
   * };
   * async.mapValues(array, iterator, function(err, res) {
   *   console.log(res); // { '0': 1, '1': 3, '2': 2 }
   *   console.log(order); // [[1, 0], [2, 2], [3, 1]]
   * });
   *
   * @example
   *
   * // object
   * var order = [];
   * var object = { a: 1, b: 3, c: 2 };
   * var iterator = function(num, done) {
   *   setTimeout(function() {
   *     order.push(num);
   *     done(null, num);
   *   }, num * 10);
   * };
   * async.mapValues(object, iterator, function(err, res) {
   *   console.log(res); // { a: 1, b: 3, c: 2 }
   *   console.log(order); // [1, 2, 3]
   * });
   *
   * @example
   *
   * // object with key
   * var order = [];
   * var object = { a: 1, b: 3, c: 2 };
   * var iterator = function(num, key, done) {
   *   setTimeout(function() {
   *     order.push([num, key]);
   *     done(null, num);
   *   }, num * 10);
   * };
   * async.mapValues(object, iterator, function(err, res) {
   *   console.log(res); // { a: 1, b: 3, c: 2 }
   *   console.log(order); // [[1, 'a'], [2, 'c'], [3, 'b']]
   * });
   *
   */
  var mapValues = createMap(arrayEachIndex, baseEachKey, symbolEachKey, false);

  /**
   * @memberof async
   * @namespace filter
   * @param {Array|Object} collection
   * @param {Function} iterator
   * @param {Function} callback
   * @example
   *
   * // array
   * var order = [];
   * var array = [1, 3, 2];
   * var iterator = function(num, done) {
   *   setTimeout(function() {
   *     order.push(num);
   *     done(null, num % 2);
   *   }, num * 10);
   * };
   * async.filter(array, iterator, function(err, res) {
   *   console.log(res); // [1, 3];
   *   console.log(order); // [1, 2, 3]
   * });
   *
   * @example
   *
   * // array with index
   * var order = [];
   * var array = [1, 3, 2];
   * var iterator = function(num, index, done) {
   *   setTimeout(function() {
   *     order.push([num, index]);
   *     done(null, num % 2);
   *   }, num * 10);
   * };
   * async.filter(array, iterator, function(err, res) {
   *   console.log(res); // [1, 3];
   *   console.log(order); // [[1, 0], [2, 2], [3, 1]]
   * });
   *
   * @example
   *
   * // object
   * var order = [];
   * var object = { a: 1, b: 3, c: 2 };
   * var iterator = function(num, done) {
   *   setTimeout(function() {
   *     order.push(num);
   *     done(null, num % 2);
   *   }, num * 10);
   * };
   * async.filter(object, iterator, function(err, res) {
   *   console.log(res); // [1, 3];
   *   console.log(order); // [1, 2, 3]
   * });
   *
   * @example
   *
   * // object with key
   * var order = [];
   * var object = { a: 1, b: 3, c: 2 };
   * var iterator = function(num, key, done) {
   *   setTimeout(function() {
   *     order.push([num, key]);
   *     done(null, num % 2);
   *   }, num * 10);
   * };
   * async.filter(object, iterator, function(err, res) {
   *   console.log(res); // [1, 3];
   *   console.log(order); // [[1, 'a'], [2, 'c'], [3, 'b']]
   * });
   *
   */
  var filter = createFilter(arrayEachIndexValue, baseEachIndexValue, symbolEachIndexValue, true);

  /**
   * @memberof async
   * @namespace filterSeries
   * @param {Array|Object} collection
   * @param {Function} iterator
   * @param {Function} callback
   * @example
   *
   * // array
   * var order = [];
   * var array = [1, 3, 2];
   * var iterator = function(num, done) {
   *   setTimeout(function() {
   *     order.push(num);
   *     done(null, num % 2);
   *   }, num * 10);
   * };
   * async.filterSeries(array, iterator, function(err, res) {
   *   console.log(res); // [1, 3];
   *   console.log(order); // [1, 3, 2]
   * });
   *
   * @example
   *
   * // array with index
   * var order = [];
   * var array = [1, 3, 2];
   * var iterator = function(num, index, done) {
   *   setTimeout(function() {
   *     order.push([num, index]);
   *     done(null, num % 2);
   *   }, num * 10);
   * };
   * async.filterSeries(array, iterator, function(err, res) {
   *   console.log(res); // [1, 3]
   *   console.log(order); // [[1, 0], [3, 1], [2, 2]]
   * });
   *
   * @example
   *
   * // object
   * var order = [];
   * var object = { a: 1, b: 3, c: 2 };
   * var iterator = function(num, done) {
   *   setTimeout(function() {
   *     order.push(num);
   *     done(null, num % 2);
   *   }, num * 10);
   * };
   * async.filterSeries(object, iterator, function(err, res) {
   *   console.log(res); // [1, 3]
   *   console.log(order); // [1, 3, 2]
   * });
   *
   * @example
   *
   * // object with key
   * var order = [];
   * var object = { a: 1, b: 3, c: 2 };
   * var iterator = function(num, key, done) {
   *   setTimeout(function() {
   *     order.push([num, key]);
   *     done(null, num % 2);
   *   }, num * 10);
   * };
   * async.filterSeries(object, iterator, function(err, res) {
   *   console.log(res); // [1, 3]
   *   console.log(order); // [[1, 'a'], [3, 'b'], [2, 'c']]
   * });
   *
   */
  var filterSeries = createFilterSeries(true);

  /**
   * @memberof async
   * @namespace filterLimit
   * @param {Array|Object} collection
   * @param {number} limit - limit >= 1
   * @param {Function} iterator
   * @param {Function} callback
   * @example
   *
   * // array
   * var order = [];
   * var array = [1, 5, 3, 4, 2];
   * var iterator = function(num, done) {
   *   setTimeout(function() {
   *     order.push(num);
   *     done(null, num % 2);
   *   }, num * 10);
   * };
   * async.filterLimit(array, 2, iterator, function(err, res) {
   *   console.log(res); // [1, 5, 3]
   *   console.log(order); // [1, 3, 5, 2, 4]
   * });
   *
   * @example
   *
   * // array with index
   * var order = [];
   * var array = [1, 5, 3, 4, 2];
   * var iterator = function(num, index, done) {
   *   setTimeout(function() {
   *     order.push([num, index]);
   *     done(null, num % 2);
   *   }, num * 10);
   * };
   * async.filterLimit(array, 2, iterator, function(err, res) {
   *   console.log(res); // [1, 5, 3]
   *   console.log(order); // [[1, 0], [3, 2], [5, 1], [2, 4], [4, 3]]
   * });
   *
   * @example
   *
   * // object
   * var order = [];
   * var object = { a: 1, b: 5, c: 3, d: 4, e: 2 };
   * var iterator = function(num, done) {
   *   setTimeout(function() {
   *     order.push(num);
   *     done(null, num % 2);
   *   }, num * 10);
   * };
   * async.filterLimit(object, 2, iterator, function(err, res) {
   *   console.log(res); // [1, 5, 3]
   *   console.log(order); // [1, 3, 5, 2, 4]
   * });
   *
   * @example
   *
   * // object with key
   * var order = [];
   * var object = { a: 1, b: 5, c: 3, d: 4, e: 2 };
   * var iterator = function(num, key, done) {
   *   setTimeout(function() {
   *     order.push([num, key]);
   *     done(null, num % 2);
   *   }, num * 10);
   * };
   * async.filterLimit(object, 2, iterator, function(err, res) {
   *   console.log(res); // [1, 5, 3]
   *   console.log(order); // [[1, 'a'], [3, 'c'], [5, 'b'], [2, 'e'], [4, 'd']]
   * });
   *
   */
  var filterLimit = createFilterLimit(true);

  /**
   * @memberof async
   * @namespace reject
   * @param {Array|Object} collection
   * @param {Function} iterator
   * @param {Function} callback
   * @example
   *
   * // array
   * var order = [];
   * var array = [1, 3, 2];
   * var iterator = function(num, done) {
   *   setTimeout(function() {
   *     order.push(num);
   *     done(null, num % 2);
   *   }, num * 10);
   * };
   * async.reject(array, iterator, function(err, res) {
   *   console.log(res); // [2];
   *   console.log(order); // [1, 2, 3]
   * });
   *
   * @example
   *
   * // array with index
   * var order = [];
   * var array = [1, 3, 2];
   * var iterator = function(num, index, done) {
   *   setTimeout(function() {
   *     order.push([num, index]);
   *     done(null, num % 2);
   *   }, num * 10);
   * };
   * async.reject(array, iterator, function(err, res) {
   *   console.log(res); // [2];
   *   console.log(order); // [[1, 0], [2, 2], [3, 1]]
   * });
   *
   * @example
   *
   * // object
   * var order = [];
   * var object = { a: 1, b: 3, c: 2 };
   * var iterator = function(num, done) {
   *   setTimeout(function() {
   *     order.push(num);
   *     done(null, num % 2);
   *   }, num * 10);
   * };
   * async.reject(object, iterator, function(err, res) {
   *   console.log(res); // [2];
   *   console.log(order); // [1, 2, 3]
   * });
   *
   * @example
   *
   * // object with key
   * var order = [];
   * var object = { a: 1, b: 3, c: 2 };
   * var iterator = function(num, key, done) {
   *   setTimeout(function() {
   *     order.push([num, key]);
   *     done(null, num % 2);
   *   }, num * 10);
   * };
   * async.reject(object, iterator, function(err, res) {
   *   console.log(res); // [2];
   *   console.log(order); // [[1, 'a'], [2, 'c'], [3, 'b']]
   * });
   *
   */
  var reject = createFilter(arrayEachIndexValue, baseEachIndexValue, symbolEachIndexValue, false);

  /**
   * @memberof async
   * @namespace rejectSeries
   * @param {Array|Object} collection
   * @param {Function} iterator
   * @param {Function} callback
   * @example
   *
   * // array
   * var order = [];
   * var array = [1, 3, 2];
   * var iterator = function(num, done) {
   *   setTimeout(function() {
   *     order.push(num);
   *     done(null, num % 2);
   *   }, num * 10);
   * };
   * async.rejectSeries(array, iterator, function(err, res) {
   *   console.log(res); // [2];
   *   console.log(order); // [1, 3, 2]
   * });
   *
   * @example
   *
   * // object
   * var order = [];
   * var object = { a: 1, b: 3, c: 2 };
   * var iterator = function(num, done) {
   *   setTimeout(function() {
   *     order.push(num);
   *     done(null, num % 2);
   *   }, num * 10);
   * };
   * async.rejectSeries(object, iterator, function(err, res) {
   *   console.log(res); // [2];
   *   console.log(order); // [1, 3, 2]
   * });
   *
   * @example
   *
   * // object with key
   * var order = [];
   * var object = { a: 1, b: 3, c: 2 };
   * var iterator = function(num, key, done) {
   *   setTimeout(function() {
   *     order.push([num, key]);
   *     done(null, num % 2);
   *   }, num * 10);
   * };
   * async.rejectSeries(object, iterator, function(err, res) {
   *   console.log(res); // [2];
   *   console.log(order); // [[1, 'a'], [3, 'b'], [2, 'c']]
   * });
   *
   */
  var rejectSeries = createFilterSeries(false);

  /**
   * @memberof async
   * @namespace rejectLimit
   * @param {Array|Object} collection
   * @param {number} limit - limit >= 1
   * @param {Function} iterator
   * @param {Function} callback
   * @example
   *
   * // array
   * var order = [];
   * var array = [1, 5, 3, 4, 2];
   * var iterator = function(num, done) {
   *   setTimeout(function() {
   *     order.push(num);
   *     done(null, num % 2);
   *   }, num * 10);
   * };
   * async.rejectLimit(array, 2, iterator, function(err, res) {
   *   console.log(res); // [4, 2]
   *   console.log(order); // [1, 3, 5, 2, 4]
   * });
   *
   * @example
   *
   * // array with index
   * var order = [];
   * var array = [1, 5, 3, 4, 2];
   * var iterator = function(num, index, done) {
   *   setTimeout(function() {
   *     order.push([num, index]);
   *     done(null, num % 2);
   *   }, num * 10);
   * };
   * async.rejectLimit(array, 2, iterator, function(err, res) {
   *   console.log(res); // [4, 2]
   *   console.log(order); // [[1, 0], [3, 2], [5, 1], [2, 4], [4, 3]]
   * });
   *
   * @example
   *
   * // object
   * var order = [];
   * var object = { a: 1, b: 5, c: 3, d: 4, e: 2 };
   * var iterator = function(num, done) {
   *   setTimeout(function() {
   *     order.push(num);
   *     done(null, num % 2);
   *   }, num * 10);
   * };
   * async.rejectLimit(object, 2, iterator, function(err, res) {
   *   console.log(res); // [4, 2]
   *   console.log(order); // [1, 3, 5, 2, 4]
   * });
   *
   * @example
   *
   * // object with key
   * var order = [];
   * var object = { a: 1, b: 5, c: 3, d: 4, e: 2 };
   * var iterator = function(num, key, done) {
   *   setTimeout(function() {
   *     order.push([num, key]);
   *     done(null, num % 2);
   *   }, num * 10);
   * };
   * async.rejectLimit(object, 2, iterator, function(err, res) {
   *   console.log(res); // [4, 2]
   *   console.log(order); // [[1, 'a'], [3, 'c'], [5, 'b'], [2, 'e'], [4, 'd']]
   * });
   *
   */
  var rejectLimit = createFilterLimit(false);

  /**
   * @memberof async
   * @namespace detect
   * @param {Array|Object} collection
   * @param {Function} iterator
   * @param {Function} callback
   * @example
   *
   * // array
   * var order = [];
   * var array = [1, 3, 2];
   * var iterator = function(num, done) {
   *   setTimeout(function() {
   *     order.push(num);
   *     done(null, num % 2);
   *   }, num * 10);
   * };
   * async.detect(array, iterator, function(err, res) {
   *   console.log(res); // 1
   *   console.log(order); // [1]
   * });
   *
   * @example
   *
   * // array with index
   * var order = [];
   * var array = [1, 3, 2];
   * var iterator = function(num, index, done) {
   *   setTimeout(function() {
   *     order.push([num, index]);
   *     done(null, num % 2);
   *   }, num * 10);
   * };
   * async.detect(array, iterator, function(err, res) {
   *   console.log(res); // 1
   *   console.log(order); // [[1, 0]]
   * });
   *
   * @example
   *
   * // object
   * var order = [];
   * var object = { a: 1, b: 3, c: 2 };
   * var iterator = function(num, done) {
   *   setTimeout(function() {
   *     order.push(num);
   *     done(null, num % 2);
   *   }, num * 10);
   * };
   * async.detect(object, iterator, function(err, res) {
   *   console.log(res); // 1
   *   console.log(order); // [1]
   * });
   *
   * @example
   *
   * // object with key
   * var order = [];
   * var object = { a: 1, b: 3, c: 2 };
   * var iterator = function(num, key, done) {
   *   setTimeout(function() {
   *     order.push([num, key]);
   *     done(null, num % 2);
   *   }, num * 10);
   * };
   * async.detect(object, iterator, function(err, res) {
   *   console.log(res); // 1
   *   console.log(order); // [[1, 'a']]
   * });
   *
   */
  var detect = createDetect(arrayEachValue, baseEachValue, symbolEachValue, true);

  /**
   * @memberof async
   * @namespace detectSeries
   * @param {Array|Object} collection
   * @param {Function} iterator
   * @param {Function} callback
   * @example
   *
   * // array
   * var order = [];
   * var array = [1, 3, 2];
   * var iterator = function(num, done) {
   *   setTimeout(function() {
   *     order.push(num);
   *     done(null, num % 2);
   *   }, num * 10);
   * };
   * async.detectSeries(array, iterator, function(err, res) {
   *   console.log(res); // 1
   *   console.log(order); // [1]
   * });
   *
   * @example
   *
   * // array with index
   * var order = [];
   * var array = [1, 3, 2];
   * var iterator = function(num, index, done) {
   *   setTimeout(function() {
   *     order.push([num, index]);
   *     done(null, num % 2);
   *   }, num * 10);
   * };
   * async.detectSeries(array, iterator, function(err, res) {
   *   console.log(res); // 1
   *   console.log(order); // [[1, 0]]
   * });
   *
   * @example
   *
   * // object
   * var order = [];
   * var object = { a: 1, b: 3, c: 2 };
   * var iterator = function(num, done) {
   *   setTimeout(function() {
   *     order.push(num);
   *     done(null, num % 2);
   *   }, num * 10);
   * };
   * async.detectSeries(object, iterator, function(err, res) {
   *   console.log(res); // 1
   *   console.log(order); // [1]
   * });
   *
   * @example
   *
   * // object with key
   * var order = [];
   * var object = { a: 1, b: 3, c: 2 };
   * var iterator = function(num, key, done) {
   *   setTimeout(function() {
   *     order.push([num, key]);
   *     done(null, num % 2);
   *   }, num * 10);
   * };
   * async.detectSeries(object, iterator, function(err, res) {
   *   console.log(res); // 1
   *   console.log(order); // [[1, 'a']]
   * });
   *
   */
  var detectSeries = createDetectSeries(true);

  /**
   * @memberof async
   * @namespace detectLimit
   * @param {Array|Object} collection
   * @param {number} limit - limit >= 1
   * @param {Function} iterator
   * @param {Function} callback
   * @example
   *
   * // array
   * var order = [];
   * var array = [1, 5, 3, 4, 2];
   * var iterator = function(num, done) {
   *   setTimeout(function() {
   *     order.push(num);
   *     done(null, num % 2);
   *   }, num * 10);
   * };
   * async.detectLimit(array, 2, iterator, function(err, res) {
   *   console.log(res); // 1
   *   console.log(order); // [1]
   * });
   *
   * @example
   *
   * // array with index
   * var order = [];
   * var array = [1, 5, 3, 4, 2];
   * var iterator = function(num, index, done) {
   *   setTimeout(function() {
   *     order.push([num, index]);
   *     done(null, num % 2);
   *   }, num * 10);
   * };
   * async.detectLimit(array, 2, iterator, function(err, res) {
   *   console.log(res); // 1
   *   console.log(order); // [[1, 0]]
   * });
   *
   * @example
   *
   * // object
   * var order = [];
   * var object = { a: 1, b: 5, c: 3, d: 4, e: 2 };
   * var iterator = function(num, done) {
   *   setTimeout(function() {
   *     order.push(num);
   *     done(null, num % 2);
   *   }, num * 10);
   * };
   * async.detectLimit(object, 2, iterator, function(err, res) {
   *   console.log(res); // 1
   *   console.log(order); // [1]
   * });
   *
   * @example
   *
   * // object with key
   * var order = [];
   * var object = { a: 1, b: 5, c: 3, d: 4, e: 2 };
   * var iterator = function(num, key, done) {
   *   setTimeout(function() {
   *     order.push([num, key]);
   *     done(null, num % 2);
   *   }, num * 10);
   * };
   * async.detectLimit(object, 2, iterator, function(err, res) {
   *   console.log(res); // 1
   *   console.log(order); // [[1, 'a']]
   * });
   *
   */
  var detectLimit = createDetectLimit(true);

  /**
   * @memberof async
   * @namespace every
   * @param {Array|Object} collection
   * @param {Function} iterator
   * @param {Function} callback
   * @example
   *
   * // array
   * var order = [];
   * var array = [1, 3, 2];
   * var iterator = function(num, done) {
   *   setTimeout(function() {
   *     order.push(num);
   *     done(null, num % 2);
   *   }, num * 10);
   * };
   * async.every(array, iterator, function(err, res) {
   *   console.log(res); // false
   *   console.log(order); // [1, 2]
   * });
   *
   * @example
   *
   * // array with index
   * var order = [];
   * var array = [1, 3, 2];
   * var iterator = function(num, index, done) {
   *   setTimeout(function() {
   *     order.push([num, index]);
   *     done(null, num % 2);
   *   }, num * 10);
   * };
   * async.every(array, iterator, function(err, res) {
   *   console.log(res); // false
   *   console.log(order); // [[1, 0], [2, 2]]
   * });
   *
   * @example
   *
   * // object
   * var order = [];
   * var object = { a: 1, b: 3, c: 2 };
   * var iterator = function(num, done) {
   *   setTimeout(function() {
   *     order.push(num);
   *     done(null, num % 2);
   *   }, num * 10);
   * };
   * async.every(object, iterator, function(err, res) {
   *   console.log(res); // false
   *   console.log(order); // [1, 2]
   * });
   *
   * @example
   *
   * // object with key
   * var order = [];
   * var object = { a: 1, b: 3, c: 2 };
   * var iterator = function(num, key, done) {
   *   setTimeout(function() {
   *     order.push([num, key]);
   *     done(null, num % 2);
   *   }, num * 10);
   * };
   * async.every(object, iterator, function(err, res) {
   *   console.log(res); // false
   *   console.log(order); // [[1, 'a'], [2, 'c']]
   * });
   *
   */
  var every = createEvery(arrayEachValue, baseEachValue, symbolEachValue);

  /**
   * @memberof async
   * @namespace everySeries
   * @param {Array|Object} collection
   * @param {Function} iterator
   * @param {Function} callback
   * @example
   *
   * // array
   * var order = [];
   * var array = [1, 3, 2];
   * var iterator = function(num, done) {
   *   setTimeout(function() {
   *     order.push(num);
   *     done(null, num % 2);
   *   }, num * 10);
   * };
   * async.everySeries(array, iterator, function(err, res) {
   *   console.log(res); // false
   *   console.log(order); // [1, 3, 2]
   * });
   *
   * @example
   *
   * // array with index
   * var order = [];
   * var array = [1, 3, 2];
   * var iterator = function(num, index, done) {
   *   setTimeout(function() {
   *     order.push([num, index]);
   *     done(null, num % 2);
   *   }, num * 10);
   * };
   * async.everySeries(array, iterator, function(err, res) {
   *   console.log(res); // false
   *   console.log(order); // [[1, 0], [3, 1], [2, 2]]
   * });
   *
   * @example
   *
   * // object
   * var order = [];
   * var object = { a: 1, b: 3, c: 2 };
   * var iterator = function(num, done) {
   *   setTimeout(function() {
   *     order.push(num);
   *     done(null, num % 2);
   *   }, num * 10);
   * };
   * async.everySeries(object, iterator, function(err, res) {
   *   console.log(res); // false
   *   console.log(order); // [1, 3, 2]
   * });
   *
   * @example
   *
   * // object with key
   * var order = [];
   * var object = { a: 1, b: 3, c: 2 };
   * var iterator = function(num, key, done) {
   *   setTimeout(function() {
   *     order.push([num, key]);
   *     done(null, num % 2);
   *   }, num * 10);
   * };
   * async.everySeries(object, iterator, function(err, res) {
   *   console.log(res); // false
   *   console.log(order); // [[1, 'a'], [3, 'b'] [2, 'c']]
   * });
   *
   */
  var everySeries = createEverySeries();

  /**
   * @memberof async
   * @namespace everyLimit
   * @param {Array|Object} collection
   * @param {number} limit - limit >= 1
   * @param {Function} iterator
   * @param {Function} callback
   * @example
   *
   * // array
   * var order = [];
   * var array = [1, 5, 3, 4, 2];
   * var iterator = function(num, done) {
   *   setTimeout(function() {
   *     order.push(num);
   *     done(null, num % 2);
   *   }, num * 10);
   * };
   * async.everyLimit(array, 2, iterator, function(err, res) {
   *   console.log(res); // false
   *   console.log(order); // [1, 3, 5, 2]
   * });
   *
   * @example
   *
   * // array with index
   * var order = [];
   * var array = [1, 5, 3, 4, 2];
   * var iterator = function(num, index, done) {
   *   setTimeout(function() {
   *     order.push([num, index]);
   *     done(null, num % 2);
   *   }, num * 10);
   * };
   * async.everyLimit(array, 2, iterator, function(err, res) {
   *   console.log(res); // false
   *   console.log(order); // [[1, 0], [3, 2], [5, 1], [2, 4]]
   * });
   *
   * @example
   *
   * // object
   * var order = [];
   * var object = { a: 1, b: 5, c: 3, d: 4, e: 2 };
   * var iterator = function(num, done) {
   *   setTimeout(function() {
   *     order.push(num);
   *     done(null, num % 2);
   *   }, num * 10);
   * };
   * async.everyLimit(object, 2, iterator, function(err, res) {
   *   console.log(res); // false
   *   console.log(order); // [1, 3, 5, 2]
   * });
   *
   * @example
   *
   * // object with key
   * var order = [];
   * var object = { a: 1, b: 5, c: 3, d: 4, e: 2 };
   * var iterator = function(num, key, done) {
   *   setTimeout(function() {
   *     order.push([num, key]);
   *     done(null, num % 2);
   *   }, num * 10);
   * };
   * async.everyLimit(object, 2, iterator, function(err, res) {
   *   console.log(res); // false
   *   console.log(order); // [[1, 'a'], [3, 'c'], [5, 'b'], [2, 'e']]
   * });
   *
   */
  var everyLimit = createEveryLimit();

  /**
   * @memberof async
   * @namespace pick
   * @param {Array|Object} collection
   * @param {Function} iterator
   * @param {Function} callback
   * @example
   *
   * // array
   * var order = [];
   * var array = [1, 3, 2, 4];
   * var iterator = function(num, done) {
   *   setTimeout(function() {
   *     order.push(num);
   *     done(null, num % 2);
   *   }, num * 10);
   * };
   * async.pick(array, iterator, function(err, res) {
   *   console.log(res); // { '0': 1, '1': 3 }
   *   console.log(order); // [1, 2, 3, 4]
   * });
   *
   * @example
   *
   * // array with index
   * var order = [];
   * var array = [1, 3, 2, 4];
   * var iterator = function(num, index, done) {
   *   setTimeout(function() {
   *     order.push([num, index]);
   *     done(null, num % 2);
   *   }, num * 10);
   * };
   * async.pick(array, iterator, function(err, res) {
   *   console.log(res); // { '0': 1, '1': 3 }
   *   console.log(order); // [[0, 1], [2, 2], [3, 1], [4, 3]]
   * });
   *
   * @example
   *
   * // object
   * var order = [];
   * var object = { a: 1, b: 3, c: 2, d: 4 };
   * var iterator = function(num, done) {
   *   setTimeout(function() {
   *     order.push(num);
   *     done(null, num % 2);
   *   }, num * 10);
   * };
   * async.pick(object, iterator, function(err, res) {
   *   console.log(res); // { a: 1, b: 3 }
   *   console.log(order); // [1, 2, 3, 4]
   * });
   *
   * @example
   *
   * // object with key
   * var order = [];
   * var object = { a: 1, b: 3, c: 2, d: 4 };
   * var iterator = function(num, key, done) {
   *   setTimeout(function() {
   *     order.push([num, key]);
   *     done(null, num % 2);
   *   }, num * 10);
   * };
   * async.pick(object, iterator, function(err, res) {
   *   console.log(res); // { a: 1, b: 3 }
   *   console.log(order); // [[1, 'a'], [2, 'c'], [3, 'b'], [4, 'd']]
   * });
   *
   */
  var pick = createPick(arrayEachIndexValue, baseEachKeyValue, symbolEachKeyValue, true);

  /**
   * @memberof async
   * @namespace pickSeries
   * @param {Array|Object} collection
   * @param {Function} iterator
   * @param {Function} callback
   * @example
   *
   * // array
   * var order = [];
   * var array = [1, 3, 2, 4];
   * var iterator = function(num, done) {
   *   setTimeout(function() {
   *     order.push(num);
   *     done(null, num % 2);
   *   }, num * 10);
   * };
   * async.pickSeries(array, iterator, function(err, res) {
   *   console.log(res); // { '0': 1, '1': 3 }
   *   console.log(order); // [1, 3, 2, 4]
   * });
   *
   * @example
   *
   * // array with index
   * var order = [];
   * var array = [1, 3, 2, 4];
   * var iterator = function(num, index, done) {
   *   setTimeout(function() {
   *     order.push([num, index]);
   *     done(null, num % 2);
   *   }, num * 10);
   * };
   * async.pickSeries(array, iterator, function(err, res) {
   *   console.log(res); // { '0': 1, '1': 3 }
   *   console.log(order); // [[0, 1], [3, 1], [2, 2], [4, 3]]
   * });
   *
   * @example
   *
   * // object
   * var order = [];
   * var object = { a: 1, b: 3, c: 2, d: 4 };
   * var iterator = function(num, done) {
   *   setTimeout(function() {
   *     order.push(num);
   *     done(null, num % 2);
   *   }, num * 10);
   * };
   * async.pickSeries(object, iterator, function(err, res) {
   *   console.log(res); // { a: 1, b: 3 }
   *   console.log(order); // [1, 3, 2, 4]
   * });
   *
   * @example
   *
   * // object with key
   * var order = [];
   * var object = { a: 1, b: 3, c: 2, d: 4 };
   * var iterator = function(num, key, done) {
   *   setTimeout(function() {
   *     order.push([num, key]);
   *     done(null, num % 2);
   *   }, num * 10);
   * };
   * async.pickSeries(object, iterator, function(err, res) {
   *   console.log(res); // { a: 1, b: 3 }
   *   console.log(order); // [[1, 'a'], [3, 'b'], [2, 'c'], [4, 'd']]
   * });
   *
   */
  var pickSeries = createPickSeries(true);

  /**
   * @memberof async
   * @namespace pickLimit
   * @param {Array|Object} collection
   * @param {number} limit - limit >= 1
   * @param {Function} iterator
   * @param {Function} callback
   * @example
   *
   * // array
   * var order = [];
   * var array = [1, 5, 3, 4, 2];
   * var iterator = function(num, done) {
   *   setTimeout(function() {
   *     order.push(num);
   *     done(null, num % 2);
   *   }, num * 10);
   * };
   * async.pickLimit(array, 2, iterator, function(err, res) {
   *   console.log(res); // { '0': 1, '1': 5, '2': 3 }
   *   console.log(order); // [1, 3, 5, 2, 4]
   * });
   *
   * @example
   *
   * // array with index
   * var order = [];
   * var array = [1, 5, 3, 4, 2];
   * var iterator = function(num, index, done) {
   *   setTimeout(function() {
   *     order.push([num, index]);
   *     done(null, num % 2);
   *   }, num * 10);
   * };
   * async.pickLimit(array, 2, iterator, function(err, res) {
   *   console.log(res); // { '0': 1, '1': 5, '2': 3 }
   *   console.log(order); // [[1, 0], [3, 2], [5, 1], [2, 4], [4, 3]]
   * });
   *
   * @example
   *
   * // object
   * var order = [];
   * var object = { a: 1, b: 5, c: 3, d: 4, e: 2 };
   * var iterator = function(num, done) {
   *   setTimeout(function() {
   *     order.push(num);
   *     done(null, num % 2);
   *   }, num * 10);
   * };
   * async.pickLimit(object, 2, iterator, function(err, res) {
   *   console.log(res); // { a: 1, b: 5, c: 3 }
   *   console.log(order); // [1, 3, 5, 2, 4]
   * });
   *
   * @example
   *
   * // object with key
   * var order = [];
   * var object = { a: 1, b: 5, c: 3, d: 4, e: 2 };
   * var iterator = function(num, key, done) {
   *   setTimeout(function() {
   *     order.push([num, key]);
   *     done(null, num % 2);
   *   }, num * 10);
   * };
   * async.pickLimit(object, 2, iterator, function(err, res) {
   *   console.log(res); // { a: 1, b: 5, c: 3 }
   *   console.log(order); // [[1, 'a'], [3, 'c'], [5, 'b'], [2, 'e'], [4, 'd']]
   * });
   *
   */
  var pickLimit = createPickLimit(true);

  /**
   * @memberof async
   * @namespace omit
   * @param {Array|Object} collection
   * @param {Function} iterator
   * @param {Function} callback
   * @example
   *
   * // array
   * var order = [];
   * var array = [1, 3, 2, 4];
   * var iterator = function(num, done) {
   *   setTimeout(function() {
   *     order.push(num);
   *     done(null, num % 2);
   *   }, num * 10);
   * };
   * async.omit(array, iterator, function(err, res) {
   *   console.log(res); // { '2': 2, '3': 4 }
   *   console.log(order); // [1, 2, 3, 4]
   * });
   *
   * @example
   *
   * // array with index
   * var order = [];
   * var array = [1, 3, 2, 4];
   * var iterator = function(num, index, done) {
   *   setTimeout(function() {
   *     order.push([num, index]);
   *     done(null, num % 2);
   *   }, num * 10);
   * };
   * async.omit(array, iterator, function(err, res) {
   *   console.log(res); // { '2': 2, '3': 4 }
   *   console.log(order); // [[0, 1], [2, 2], [3, 1], [4, 3]]
   * });
   *
   * @example
   *
   * // object
   * var order = [];
   * var object = { a: 1, b: 3, c: 2, d: 4 };
   * var iterator = function(num, done) {
   *   setTimeout(function() {
   *     order.push(num);
   *     done(null, num % 2);
   *   }, num * 10);
   * };
   * async.omit(object, iterator, function(err, res) {
   *   console.log(res); // { c: 2, d: 4 }
   *   console.log(order); // [1, 2, 3, 4]
   * });
   *
   * @example
   *
   * // object with key
   * var order = [];
   * var object = { a: 1, b: 3, c: 2, d: 4 };
   * var iterator = function(num, key, done) {
   *   setTimeout(function() {
   *     order.push([num, key]);
   *     done(null, num % 2);
   *   }, num * 10);
   * };
   * async.omit(object, iterator, function(err, res) {
   *   console.log(res); // { c: 2, d: 4 }
   *   console.log(order); // [[1, 'a'], [2, 'c'], [3, 'b'], [4, 'd']]
   * });
   *
   */
  var omit = createPick(arrayEachIndexValue, baseEachKeyValue, symbolEachKeyValue, false);

  /**
   * @memberof async
   * @namespace omitSeries
   * @param {Array|Object} collection
   * @param {Function} iterator
   * @param {Function} callback
   * @example
   *
   * // array
   * var order = [];
   * var array = [1, 3, 2, 4];
   * var iterator = function(num, done) {
   *   setTimeout(function() {
   *     order.push(num);
   *     done(null, num % 2);
   *   }, num * 10);
   * };
   * async.omitSeries(array, iterator, function(err, res) {
   *   console.log(res); // { '2': 2, '3': 4 }
   *   console.log(order); // [1, 3, 2, 4]
   * });
   *
   * @example
   *
   * // array with index
   * var order = [];
   * var array = [1, 3, 2, 4];
   * var iterator = function(num, index, done) {
   *   setTimeout(function() {
   *     order.push([num, index]);
   *     done(null, num % 2);
   *   }, num * 10);
   * };
   * async.omitSeries(array, iterator, function(err, res) {
   *   console.log(res); // { '2': 2, '3': 4 }
   *   console.log(order); // [[0, 1], [3, 1], [2, 2], [4, 3]]
   * });
   *
   * @example
   *
   * // object
   * var order = [];
   * var object = { a: 1, b: 3, c: 2, d: 4 };
   * var iterator = function(num, done) {
   *   setTimeout(function() {
   *     order.push(num);
   *     done(null, num % 2);
   *   }, num * 10);
   * };
   * async.omitSeries(object, iterator, function(err, res) {
   *   console.log(res); // { c: 2, d: 4 }
   *   console.log(order); // [1, 3, 2, 4]
   * });
   *
   * @example
   *
   * // object with key
   * var order = [];
   * var object = { a: 1, b: 3, c: 2, d: 4 };
   * var iterator = function(num, key, done) {
   *   setTimeout(function() {
   *     order.push([num, key]);
   *     done(null, num % 2);
   *   }, num * 10);
   * };
   * async.omitSeries(object, iterator, function(err, res) {
   *   console.log(res); // { c: 2, d: 4 }
   *   console.log(order); // [[1, 'a'], [3, 'b'], [2, 'c'], [4, 'd']]
   * });
   *
   */
  var omitSeries = createPickSeries(false);

  /**
   * @memberof async
   * @namespace omitLimit
   * @param {Array|Object} collection
   * @param {number} limit - limit >= 1
   * @param {Function} iterator
   * @param {Function} callback
   * @example
   *
   * // array
   * var order = [];
   * var array = [1, 5, 3, 4, 2];
   * var iterator = function(num, done) {
   *   setTimeout(function() {
   *     order.push(num);
   *     done(null, num % 2);
   *   }, num * 10);
   * };
   * async.omitLimit(array, 2, iterator, function(err, res) {
   *   console.log(res); // { '3': 4, '4': 2 }
   *   console.log(order); // [1, 3, 5, 2, 4]
   * });
   *
   * @example
   *
   * // array with index
   * var order = [];
   * var array = [1, 5, 3, 4, 2];
   * var iterator = function(num, index, done) {
   *   setTimeout(function() {
   *     order.push([num, index]);
   *     done(null, num % 2);
   *   }, num * 10);
   * };
   * async.omitLimit(array, 2, iterator, function(err, res) {
   *   console.log(res); // { '3': 4, '4': 2 }
   *   console.log(order); // [[1, 0], [3, 2], [5, 1], [2, 4], [4, 3]]
   * });
   *
   * @example
   *
   * // object
   * var order = [];
   * var object = { a: 1, b: 5, c: 3, d: 4, e: 2 };
   * var iterator = function(num, done) {
   *   setTimeout(function() {
   *     order.push(num);
   *     done(null, num % 2);
   *   }, num * 10);
   * };
   * async.omitLimit(object, 2, iterator, function(err, res) {
   *   console.log(res); // { d: 4, e: 2 }
   *   console.log(order); // [1, 3, 5, 2, 4]
   * });
   *
   * @example
   *
   * // object with key
   * var order = [];
   * var object = { a: 1, b: 5, c: 3, d: 4, e: 2 };
   * var iterator = function(num, key, done) {
   *   setTimeout(function() {
   *     order.push([num, key]);
   *     done(null, num % 2);
   *   }, num * 10);
   * };
   * async.omitLimit(object, 2, iterator, function(err, res) {
   *   console.log(res); // { d: 4, e: 2 }
   *   console.log(order); // [[1, 'a'], [3, 'c'], [5, 'b'], [2, 'e'], [4, 'd']]
   * });
   *
   */
  var omitLimit = createPickLimit(false);

  /**
   * @memberof async
   * @namespace transform
   * @param {Array|Object} collection
   * @param {Array|Object|Function} [accumulator]
   * @param {Function} [iterator]
   * @param {Function} [callback]
   * @example
   *
   * // array
   * var order = [];
   * var collection = [1, 3, 2, 4];
   * var iterator = function(result, num, done) {
   *   setTimeout(function() {
   *     order.push(num);
   *     result.push(num)
   *     done();
   *   }, num * 10);
   * };
   * async.transform(collection, iterator, function(err, res) {
   *   console.log(res); // [1, 2, 3, 4]
   *   console.log(order); // [1, 2, 3, 4]
   * });
   *
   * @example
   *
   * // array with index and accumulator
   * var order = [];
   * var collection = [1, 3, 2, 4];
   * var iterator = function(result, num, index, done) {
   *   setTimeout(function() {
   *     order.push([num, index]);
   *     result[index] = num;
   *     done();
   *   }, num * 10);
   * };
   * async.transform(collection, {}, iterator, function(err, res) {
   *   console.log(res); // { '0': 1, '1': 3, '2': 2, '3': 4 }
   *   console.log(order); // [[1, 0], [2, 2], [3, 1], [4, 3]]
   * });
   *
   * @example
   *
   * // object with accumulator
   * var order = [];
   * var object = { a: 1, b: 3, c: 2, d: 4 };
   * var iterator = function(result, num, done) {
   *   setTimeout(function() {
   *     order.push(num);
   *     result.push(num);
   *     done();
   *   }, num * 10);
   * };
   * async.transform(collection, [], iterator, function(err, res) {
   *   console.log(res); // [1, 2, 3, 4]
   *   console.log(order); // [1, 2, 3, 4]
   * });
   *
   * @example
   *
   * // object with key
   * var order = [];
   * var object = { a: 1, b: 3, c: 2, d: 4 };
   * var iterator = function(result, num, key, done) {
   *   setTimeout(function() {
   *     order.push([num, key]);
   *     result[key] = num;
   *     done();
   *   }, num * 10);
   * };
   * async.transform(collection, iterator, function(err, res) {
   *   console.log(res); //  { a: 1, b: 3, c: 2, d: 4 }
   *   console.log(order); // [[1, 'a'], [2, 'c'], [3, 'b'], [4, 'd']]
   * });
   *
   */
  var transform = createTransform(arrayEachResult, baseEachResult, symbolEachResult);

  /**
   * @memberof async
   * @namespace sortBy
   * @param {Array|Object} collection
   * @param {Function} iterator
   * @param {Function} callback
   * @example
   *
   * // array
   * var order = [];
   * var array = [1, 3, 2];
   * var iterator = function(num, done) {
   *   setTimeout(function() {
   *     order.push(num);
   *     done(null, num);
   *   }, num * 10);
   * };
   * async.sortBy(array, iterator, function(err, res) {
   *   console.log(res); // [1, 2, 3];
   *   console.log(order); // [1, 2, 3]
   * });
   *
   * @example
   *
   * // array with index
   * var order = [];
   * var array = [1, 3, 2];
   * var iterator = function(num, index, done) {
   *   setTimeout(function() {
   *     order.push([num, index]);
   *     done(null, num);
   *   }, num * 10);
   * };
   * async.sortBy(array, iterator, function(err, res) {
   *   console.log(res); // [1, 2, 3]
   *   console.log(order); // [[1, 0], [2, 2], [3, 1]]
   * });
   *
   * @example
   *
   * // object
   * var order = [];
   * var object = { a: 1, b: 3, c: 2 };
   * var iterator = function(num, done) {
   *   setTimeout(function() {
   *     order.push(num);
   *     done(null, num);
   *   }, num * 10);
   * };
   * async.sortBy(object, iterator, function(err, res) {
   *   console.log(res); // [1, 2, 3]
   *   console.log(order); // [1, 2, 3]
   * });
   *
   * @example
   *
   * // object with key
   * var order = [];
   * var object = { a: 1, b: 3, c: 2 };
   * var iterator = function(num, key, done) {
   *   setTimeout(function() {
   *     order.push([num, key]);
   *     done(null, num);
   *   }, num * 10);
   * };
   * async.sortBy(object, iterator, function(err, res) {
   *   console.log(res); // [1, 2, 3]
   *   console.log(order); // [[1, 'a'], [2, 'c'], [3, 'b']]
   * });
   *
   */
  var sortBy = createSortBy(arrayEachIndexValue, baseEachIndexValue, symbolEachIndexValue);

  /**
   * @memberof async
   * @namespace concat
   * @param {Array|Object} collection
   * @param {Function} iterator
   * @param {Function} callback
   * @example
   *
   * // array
   * var order = [];
   * var array = [1, 3, 2];
   * var iterator = function(num, done) {
   *   setTimeout(function() {
   *     order.push(num);
   *     done(null, [num]);
   *   }, num * 10);
   * };
   * async.concat(array, iterator, function(err, res) {
   *   console.log(res); // [1, 2, 3];
   *   console.log(order); // [1, 2, 3]
   * });
   *
   * @example
   *
   * // array with index
   * var order = [];
   * var array = [1, 3, 2];
   * var iterator = function(num, index, done) {
   *   setTimeout(function() {
   *     order.push([num, index]);
   *     done(null, [num]);
   *   }, num * 10);
   * };
   * async.concat(array, iterator, function(err, res) {
   *   console.log(res); // [1, 2, 3]
   *   console.log(order); // [[1, 0], [2, 2], [3, 1]]
   * });
   *
   * @example
   *
   * // object
   * var order = [];
   * var object = { a: 1, b: 3, c: 2 };
   * var iterator = function(num, done) {
   *   setTimeout(function() {
   *     order.push(num);
   *     done(null, [num]);
   *   }, num * 10);
   * };
   * async.concat(object, iterator, function(err, res) {
   *   console.log(res); // [1, 2, 3]
   *   console.log(order); // [1, 2, 3]
   * });
   *
   * @example
   *
   * // object with key
   * var order = [];
   * var object = { a: 1, b: 3, c: 2 };
   * var iterator = function(num, key, done) {
   *   setTimeout(function() {
   *     order.push([num, key]);
   *     done(null, [num]);
   *   }, num * 10);
   * };
   * async.concat(object, iterator, function(err, res) {
   *   console.log(res); // [1, 2, 3]
   *   console.log(order); // [[1, 'a'], [2, 'c'], [3, 'b']]
   * });
   *
   */
  var concat = createConcat(arrayEachIndex, baseEachIndex, symbolEachIndex);

  /**
   * @memberof async
   * @namespace groupBy
   * @param {Array|Object} collection
   * @param {Function} iterator
   * @param {Function} callback
   * @example
   *
   * // array
   * var order = [];
   * var array = [4.2, 6.4, 6.1];
   * var iterator = function(num, done) {
   *   setTimeout(function() {
   *     order.push(num);
   *     done(null, Math.floor(num));
   *   }, num * 10);
   * };
   * async.groupBy(array, iterator, function(err, res) {
   *   console.log(res); // { '4': [4.2], '6': [6.1, 6.4] }
   *   console.log(order); // [4.2, 6.1, 6.4]
   * });
   *
   * @example
   *
   * // array with index
   * var order = [];
   * var array = [4.2, 6.4, 6.1];
   * var iterator = function(num, index, done) {
   *   setTimeout(function() {
   *     order.push([num, index]);
   *     done(null, Math.floor(num));
   *   }, num * 10);
   * };
   * async.groupBy(array, iterator, function(err, res) {
   *   console.log(res); // { '4': [4.2], '6': [6.1, 6.4] }
   *   console.log(order); // [[4.2, 0], [6.1, 2], [6.4, 1]]
   * });
   *
   * @example
   *
   * // object
   * var order = [];
   * var object = { a: 4.2, b: 6.4, c: 6.1 };
   * var iterator = function(num, done) {
   *   setTimeout(function() {
   *     order.push(num);
   *     done(null, Math.floor(num));
   *   }, num * 10);
   * };
   * async.groupBy(object, iterator, function(err, res) {
   *   console.log(res); // { '4': [4.2], '6': [6.1, 6.4] }
   *   console.log(order); // [4.2, 6.1, 6.4]
   * });
   *
   * @example
   *
   * // object with key
   * var order = [];
   * var object = { a: 4.2, b: 6.4, c: 6.1 };
   * var iterator = function(num, key, done) {
   *   setTimeout(function() {
   *     order.push([num, key]);
   *     done(null, Math.floor(num));
   *   }, num * 10);
   * };
   * async.groupBy(object, iterator, function(err, res) {
   *   console.log(res); // { '4': [4.2], '6': [6.1, 6.4] }
   *   console.log(order); // [[4.2, 'a'], [6.1, 'c'], [6.4, 'b']]
   * });
   *
   */
  var groupBy = createGroupBy(arrayEachValue, baseEachValue, symbolEachValue);

  /**
   * @memberof async
   * @namespace parallel
   * @param {Array|Object} tasks - functions
   * @param {Function} callback
   * @example
   *
   * var order = [];
   * var tasks = [
   *  function(done) {
   *    setTimeout(function() {
   *      order.push(1);
   *      done(null, 1);
   *    }, 10);
   *  },
   *  function(done) {
   *    setTimeout(function() {
   *      order.push(2);
   *      done(null, 2);
   *    }, 30);
   *  },
   *  function(done) {
   *    setTimeout(function() {
   *      order.push(3);
   *      done(null, 3);