1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
|
import eachOfSeries from './eachOfSeries';
import once from './internal/once';
import wrapAsync from './internal/wrapAsync';
import awaitify from './internal/awaitify'
/**
* Reduces `coll` into a single value using an async `iteratee` to return each
* successive step. `memo` is the initial state of the reduction. This function
* only operates in series.
*
* For performance reasons, it may make sense to split a call to this function
* into a parallel map, and then use the normal `Array.prototype.reduce` on the
* results. This function is for situations where each step in the reduction
* needs to be async; if you can get the data before reducing it, then it's
* probably a good idea to do so.
*
* @name reduce
* @static
* @memberOf module:Collections
* @method
* @alias inject
* @alias foldl
* @category Collection
* @param {Array|Iterable|AsyncIterable|Object} coll - A collection to iterate over.
* @param {*} memo - The initial state of the reduction.
* @param {AsyncFunction} iteratee - A function applied to each item in the
* array to produce the next step in the reduction.
* The `iteratee` should complete with the next state of the reduction.
* If the iteratee complete with an error, the reduction is stopped and the
* main `callback` is immediately called with the error.
* Invoked with (memo, item, callback).
* @param {Function} [callback] - A callback which is called after all the
* `iteratee` functions have finished. Result is the reduced value. Invoked with
* (err, result).
* @returns {Promise} a promise, if no callback is passed
* @example
*
* async.reduce([1,2,3], 0, function(memo, item, callback) {
* // pointless async:
* process.nextTick(function() {
* callback(null, memo + item)
* });
* }, function(err, result) {
* // result is now equal to the last value of memo, which is 6
* });
*/
function reduce(coll, memo, iteratee, callback) {
callback = once(callback);
var _iteratee = wrapAsync(iteratee);
return eachOfSeries(coll, (x, i, iterCb) => {
_iteratee(memo, x, (err, v) => {
memo = v;
iterCb(err);
});
}, err => callback(err, memo));
}
export default awaitify(reduce, 4)
|
