73 lines
2.5 KiB
JavaScript
73 lines
2.5 KiB
JavaScript
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'use strict';
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Object.defineProperty(exports, "__esModule", {
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value: true
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});
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exports.default = reduce;
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var _eachOfSeries = require('./eachOfSeries');
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var _eachOfSeries2 = _interopRequireDefault(_eachOfSeries);
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var _noop = require('lodash/noop');
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var _noop2 = _interopRequireDefault(_noop);
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var _once = require('./internal/once');
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var _once2 = _interopRequireDefault(_once);
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function _interopRequireDefault(obj) { return obj && obj.__esModule ? obj : { default: obj }; }
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/**
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* Reduces `coll` into a single value using an async `iteratee` to return each
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* successive step. `memo` is the initial state of the reduction. This function
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* only operates in series.
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*
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* For performance reasons, it may make sense to split a call to this function
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* into a parallel map, and then use the normal `Array.prototype.reduce` on the
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* results. This function is for situations where each step in the reduction
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* needs to be async; if you can get the data before reducing it, then it's
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* probably a good idea to do so.
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*
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* @name reduce
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* @static
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* @memberOf module:Collections
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* @method
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* @alias inject
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* @alias foldl
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* @category Collection
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* @param {Array|Iterable|Object} coll - A collection to iterate over.
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* @param {*} memo - The initial state of the reduction.
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* @param {Function} iteratee - A function applied to each item in the
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* array to produce the next step in the reduction. The `iteratee` is passed a
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* `callback(err, reduction)` which accepts an optional error as its first
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* argument, and the state of the reduction as the second. If an error is
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* passed to the callback, the reduction is stopped and the main `callback` is
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* immediately called with the error. Invoked with (memo, item, callback).
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* @param {Function} [callback] - A callback which is called after all the
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* `iteratee` functions have finished. Result is the reduced value. Invoked with
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* (err, result).
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* @example
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*
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* async.reduce([1,2,3], 0, function(memo, item, callback) {
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* // pointless async:
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* process.nextTick(function() {
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* callback(null, memo + item)
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* });
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* }, function(err, result) {
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* // result is now equal to the last value of memo, which is 6
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* });
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*/
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function reduce(coll, memo, iteratee, callback) {
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callback = (0, _once2.default)(callback || _noop2.default);
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(0, _eachOfSeries2.default)(coll, function (x, i, callback) {
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iteratee(memo, x, function (err, v) {
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memo = v;
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callback(err);
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});
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}, function (err) {
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callback(err, memo);
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});
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}
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module.exports = exports['default'];
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