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
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
|
{{alias}}( collection, initial, [options,] reducer, done )
Applies a function against an accumulator and each element in a collection
and returns the accumulated result.
When invoked, `reducer` is provided a maximum of five arguments:
- `accumulator`: accumulated value
- `value`: collection value
- `index`: collection index
- `collection`: the input collection
- `next`: a callback to be invoked after processing a collection `value`
The actual number of provided arguments depends on function length. If
`reducer` accepts three arguments, `reducer` is provided:
- `accumulator`
- `value`
- `next`
If `reducer` accepts four arguments, `reducer` is provided:
- `accumulator`
- `value`
- `index`
- `next`
For every other `reducer` signature, `reducer` is provided all five
arguments.
The `next` callback accepts two arguments:
- `error`: error argument
- `accumulator`: accumulated value
If a provided function calls the `next` callback with a truthy `error`
argument, the function suspends execution and immediately calls the `done`
callback for subsequent `error` handling.
Execution is *not* guaranteed to be asynchronous. To guarantee asynchrony,
wrap the `done` callback in a function which either executes at the end of
the current stack (e.g., `nextTick`) or during a subsequent turn of the
event loop (e.g., `setImmediate`, `setTimeout`).
The function does not support dynamic collection resizing.
If provided an empty collection, the function invokes the `done` callback
with the `initial` value as the second argument.
The function does not skip `undefined` elements.
When processing collection elements concurrently, *beware* of race
conditions when updating an accumulator. This is especially true when an
accumulator is a primitive (e.g., a number). In general, prefer object
accumulators.
Parameters
----------
collection: Array|TypedArray|Object
Input collection over which to iterate. If provided an object, the
object must be array-like (excluding strings and functions).
initial: any
Accumulator value used in the first invocation of the reduction
function.
options: Object (optional)
Function options.
options.limit: integer (optional)
Maximum number of pending invocations. Default: Infinity.
options.series: boolean (optional)
Boolean indicating whether to process each collection element
sequentially. Default: true.
options.thisArg: any (optional)
Execution context.
reducer: Function
The function to invoke for each element in a collection.
done: Function
A callback invoked either upon processing all collection elements or
upon encountering an error.
Examples
--------
// Basic usage:
> function fcn( acc, value, index, next ) {
... setTimeout( onTimeout, value );
... function onTimeout() {
... console.log( value );
... acc.sum += value;
... next( null, acc );
... }
... };
> function done( error, acc ) {
... if ( error ) {
... throw error;
... }
... console.log( acc.sum );
... };
> var arr = [ 3000, 2500, 1000 ];
> var acc = { 'sum': 0 };
> {{alias}}( arr, acc, fcn, done )
3000
2500
1000
6500
// Limit number of concurrent invocations:
> function fcn( acc, value, index, next ) {
... setTimeout( onTimeout, value );
... function onTimeout() {
... console.log( value );
... acc.sum += value;
... next( null, acc );
... }
... };
> function done( error, acc ) {
... if ( error ) {
... throw error;
... }
... console.log( acc.sum );
... };
> var opts = { 'limit': 2 };
> var arr = [ 3000, 2500, 1000 ];
> var acc = { 'sum': 0 };
> {{alias}}( arr, acc, opts, fcn, done )
2500
3000
1000
6500
// Process concurrently:
> function fcn( acc, value, index, next ) {
... setTimeout( onTimeout, value );
... function onTimeout() {
... console.log( value );
... acc.sum += value;
... next( null, acc );
... }
... };
> function done( error, acc ) {
... if ( error ) {
... throw error;
... }
... console.log( acc.sum );
... };
> var opts = { 'series': false };
> var arr = [ 3000, 2500, 1000 ];
> var acc = { 'sum': 0 };
> {{alias}}( arr, acc, opts, fcn, done )
1000
2500
3000
6500
{{alias}}.factory( [options,] fcn )
Returns a function which applies a function against an accumulator and each
element in a collection and returns the accumulated result.
Parameters
----------
options: Object (optional)
Function options.
options.limit: integer (optional)
Maximum number of pending invocations. Default: Infinity.
options.series: boolean (optional)
Boolean indicating whether to process each collection element
sequentially. Default: true.
options.thisArg: any (optional)
Execution context.
fcn: Function
The function to invoke for each element in a collection.
Returns
-------
out: Function
A function which invokes a function for each element in a collection.
Examples
--------
> function fcn( acc, value, index, next ) {
... setTimeout( onTimeout, value );
... function onTimeout() {
... console.log( value );
... acc.sum += value;
... next( null, acc );
... }
... };
> var opts = { 'series': false };
> var f = {{alias}}.factory( opts, fcn );
> function done( error, acc ) {
... if ( error ) {
... throw error;
... }
... console.log( acc.sum );
... };
> var arr = [ 3000, 2500, 1000 ];
> var acc = { 'sum': 0 };
> f( arr, acc, done )
1000
2500
3000
6500
> acc = { 'sum': 0 };
> arr = [ 2000, 1500, 1000 ];
> f( arr, acc, done )
1000
1500
2000
4500
See Also
--------
|
