3 Object.defineProperty(exports, "__esModule", {
6 exports.default = reduce;
8 var _eachOfSeries = require('./eachOfSeries');
10 var _eachOfSeries2 = _interopRequireDefault(_eachOfSeries);
12 var _noop = require('lodash/noop');
14 var _noop2 = _interopRequireDefault(_noop);
16 var _once = require('./internal/once');
18 var _once2 = _interopRequireDefault(_once);
20 function _interopRequireDefault(obj) { return obj && obj.__esModule ? obj : { default: obj }; }
23 * Reduces `coll` into a single value using an async `iteratee` to return each
24 * successive step. `memo` is the initial state of the reduction. This function
25 * only operates in series.
27 * For performance reasons, it may make sense to split a call to this function
28 * into a parallel map, and then use the normal `Array.prototype.reduce` on the
29 * results. This function is for situations where each step in the reduction
30 * needs to be async; if you can get the data before reducing it, then it's
31 * probably a good idea to do so.
35 * @memberOf module:Collections
39 * @category Collection
40 * @param {Array|Iterable|Object} coll - A collection to iterate over.
41 * @param {*} memo - The initial state of the reduction.
42 * @param {Function} iteratee - A function applied to each item in the
43 * array to produce the next step in the reduction. The `iteratee` is passed a
44 * `callback(err, reduction)` which accepts an optional error as its first
45 * argument, and the state of the reduction as the second. If an error is
46 * passed to the callback, the reduction is stopped and the main `callback` is
47 * immediately called with the error. Invoked with (memo, item, callback).
48 * @param {Function} [callback] - A callback which is called after all the
49 * `iteratee` functions have finished. Result is the reduced value. Invoked with
53 * async.reduce([1,2,3], 0, function(memo, item, callback) {
55 * process.nextTick(function() {
56 * callback(null, memo + item)
58 * }, function(err, result) {
59 * // result is now equal to the last value of memo, which is 6
62 function reduce(coll, memo, iteratee, callback) {
63 callback = (0, _once2.default)(callback || _noop2.default);
64 (0, _eachOfSeries2.default)(coll, function (x, i, callback) {
65 iteratee(memo, x, function (err, v) {
73 module.exports = exports['default'];