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author | Alexander Early <alexander.early@gmail.com> | 2016-05-05 16:27:02 -0700 |
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committer | Alexander Early <alexander.early@gmail.com> | 2016-05-05 16:27:02 -0700 |
commit | 21f917ecd0485d1ffe28ae70067124e0afaf838b (patch) | |
tree | 9f125c2e3dbcbc3c4bd0bc0d63b3fd9e0b24ec19 | |
parent | bd601a4bf33bb6da2471cd634a1b41abe855397b (diff) | |
download | async-21f917ecd0485d1ffe28ae70067124e0afaf838b.tar.gz |
Add docs for transform. Closes #1134
-rw-r--r-- | README.md | 1 | ||||
-rw-r--r-- | lib/transform.js | 54 |
2 files changed, 50 insertions, 5 deletions
@@ -221,6 +221,7 @@ Some functions are also available in the following forms: * [`filter`](#filter), `filterSeries`, `filterLimit` * [`reject`](#reject), `rejectSeries`, `rejectLimit` * [`reduce`](#reduce), [`reduceRight`](#reduceRight) +* [`transform`](#transform) * [`detect`](#detect), `detectSeries`, `detectLimit` * [`sortBy`](#sortBy) * [`some`](#some), `someLimit`, `someSeries` diff --git a/lib/transform.js b/lib/transform.js index 819cd5d..cdad526 100644 --- a/lib/transform.js +++ b/lib/transform.js @@ -4,16 +4,60 @@ import isArray from 'lodash/isArray'; import eachOf from './eachOf'; -export default function transform (arr, memo, iteratee, callback) { +/** + * A relative of `reduce`. Takes an Object or Array, and iterates over each + * element in series, each step potentially mutating an `accumulator` value. + * The type of the accumulator defaults to the type of collection passed in. + * + * @name transform + * @static + * @memberOf async + * @category Collection + * @param {Array|Object} coll - A collection to iterate over. + * @param {*} [accumulator] - The initial state of the transform. If omitted, + * it will default to an empty Object or Array, depending on the type of `coll` + * @param {Function} iteratee - A function applied to each item in the + * collection that potentially modifies the accumulator. The `iteratee` is + * passed a `callback(err)` which accepts an optional error as its first + * argument. If an error is passed to the callback, the transform is stopped + * and the main `callback` is immediately called with the error. + * Invoked with (accumulator, item, key, callback). + * @param {Function} [callback] - A callback which is called after all the + * `iteratee` functions have finished. Result is the transformed accumulator. + * Invoked with (err, result). + * @example + * + * async.transform([1,2,3], function(acc, item, index, callback) { + * // pointless async: + * process.nextTick(function() { + * acc.push(item * 2) + * callback(null) + * }); + * }, function(err, result) { + * // result is now equal to [2, 4, 6] + * }); + * + * @example + * + * async.transform({a: 1, b: 2, c: 3}, function (obj, val, key, callback) { + * setImmediate(function () { + * obj[key] = val * 2; + * callback(); + * }) + * }, function (err, result) { + * // result is equal to {a: 2, b: 4, c: 6} + * }) + */ +export default function transform (arr, acc, iteratee, callback) { if (arguments.length === 3) { callback = iteratee; - iteratee = memo; - memo = isArray(arr) ? [] : {}; + iteratee = acc; + acc = isArray(arr) ? [] : {}; } eachOf(arr, function(v, k, cb) { - iteratee(memo, v, k, cb); + iteratee(acc, v, k, cb); }, function(err) { - callback(err, memo); + callback(err, acc); }); } |