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
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
|
import eachOf from './eachOf';
import once from './internal/once';
import wrapAsync from './internal/wrapAsync';
import { promiseCallback, PROMISE_SYMBOL } from './internal/promiseCallback';
/**
* A relative of `reduce`. Takes an Object or Array, and iterates over each
* element in parallel, each step potentially mutating an `accumulator` value.
* The type of the accumulator defaults to the type of collection passed in.
*
* @name transform
* @static
* @memberOf module:Collections
* @method
* @category Collection
* @param {Array|Iterable|AsyncIterable|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 {AsyncFunction} iteratee - A function applied to each item in the
* collection that potentially modifies the accumulator.
* 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).
* @returns {Promise} a promise, if no callback provided
* @example
*
* // file1.txt is a file that is 1000 bytes in size
* // file2.txt is a file that is 2000 bytes in size
* // file3.txt is a file that is 3000 bytes in size
*
* // helper function that returns human-readable size format from bytes
* function formatBytes(bytes, decimals = 2) {
* // implementation not included for brevity
* return humanReadbleFilesize;
* }
*
* const fileList = ['file1.txt','file2.txt','file3.txt'];
*
* // asynchronous function that returns the file size, transformed to human-readable format
* // e.g. 1024 bytes = 1KB, 1234 bytes = 1.21 KB, 1048576 bytes = 1MB, etc.
* function transformFileSize(acc, value, key, callback) {
* fs.stat(value, function(err, stat) {
* if (err) {
* return callback(err);
* }
* acc[key] = formatBytes(stat.size);
* callback(null);
* });
* }
*
* // Using callbacks
* async.transform(fileList, transformFileSize, function(err, result) {
* if(err) {
* console.log(err);
* } else {
* console.log(result);
* // [ '1000 Bytes', '1.95 KB', '2.93 KB' ]
* }
* });
*
* // Using Promises
* async.transform(fileList, transformFileSize)
* .then(result => {
* console.log(result);
* // [ '1000 Bytes', '1.95 KB', '2.93 KB' ]
* }).catch(err => {
* console.log(err);
* });
*
* // Using async/await
* (async () => {
* try {
* let result = await async.transform(fileList, transformFileSize);
* console.log(result);
* // [ '1000 Bytes', '1.95 KB', '2.93 KB' ]
* }
* catch (err) {
* console.log(err);
* }
* })();
*
* @example
*
* // file1.txt is a file that is 1000 bytes in size
* // file2.txt is a file that is 2000 bytes in size
* // file3.txt is a file that is 3000 bytes in size
*
* // helper function that returns human-readable size format from bytes
* function formatBytes(bytes, decimals = 2) {
* // implementation not included for brevity
* return humanReadbleFilesize;
* }
*
* const fileMap = { f1: 'file1.txt', f2: 'file2.txt', f3: 'file3.txt' };
*
* // asynchronous function that returns the file size, transformed to human-readable format
* // e.g. 1024 bytes = 1KB, 1234 bytes = 1.21 KB, 1048576 bytes = 1MB, etc.
* function transformFileSize(acc, value, key, callback) {
* fs.stat(value, function(err, stat) {
* if (err) {
* return callback(err);
* }
* acc[key] = formatBytes(stat.size);
* callback(null);
* });
* }
*
* // Using callbacks
* async.transform(fileMap, transformFileSize, function(err, result) {
* if(err) {
* console.log(err);
* } else {
* console.log(result);
* // { f1: '1000 Bytes', f2: '1.95 KB', f3: '2.93 KB' }
* }
* });
*
* // Using Promises
* async.transform(fileMap, transformFileSize)
* .then(result => {
* console.log(result);
* // { f1: '1000 Bytes', f2: '1.95 KB', f3: '2.93 KB' }
* }).catch(err => {
* console.log(err);
* });
*
* // Using async/await
* async () => {
* try {
* let result = await async.transform(fileMap, transformFileSize);
* console.log(result);
* // { f1: '1000 Bytes', f2: '1.95 KB', f3: '2.93 KB' }
* }
* catch (err) {
* console.log(err);
* }
* }
*
*/
export default function transform (coll, accumulator, iteratee, callback) {
if (arguments.length <= 3 && typeof accumulator === 'function') {
callback = iteratee;
iteratee = accumulator;
accumulator = Array.isArray(coll) ? [] : {};
}
callback = once(callback || promiseCallback());
var _iteratee = wrapAsync(iteratee);
eachOf(coll, (v, k, cb) => {
_iteratee(accumulator, v, k, cb);
}, err => callback(err, accumulator));
return callback[PROMISE_SYMBOL]
}
|
