Asynchronous Programming Library


Installation

``bash
$ npm install metasync
`

Asynchronous functions composition

metasync(fns)(data, done)

- fns - array of callback-last functions, callback contranct err-first
- data - input data (optional)
- done - err-first callback
- Returns: composed callback-last / err-first function

!composition

`js
const composed = metasync([f1, f2, f3, [[f4, f5, [f6, f7], f8]], f9]);
`

- Array of functions gives sequential execution: [f1, f2, f3]
- Double brackets array of functions gives parallel execution: [[f1, f2, f3]]

_Example:_

`js
const metasync = require('metasync');
const fs = require('fs');

// Data collector (collect keys by count)
const dc = metasync.collect(4);

dc.pick('user', { name: 'Marcus Aurelius' });
fs.readFile('HISTORY.md', (err, data) => dc.collect('history', err, data));
dc.take('readme', fs.readFile, 'README.md');
setTimeout(() => dc.pick('timer', { date: new Date() }), 1000);

// Key collector (collect certain keys by names)
const kc = metasync
.collect(['user', 'history', 'readme', 'timer'])
.timeout(2000)
.distinct()
.done((err, data) => console.log(data));

kc.pick('user', { name: 'Marcus Aurelius' });
kc.take('history', fs.readFile, 'HISTORY.md');
kc.take('readme', fs.readFile, 'README.md');
setTimeout(() => kc.pick('timer', { date: new Date() }), 1000);
`

API

$3

- fn: [][function] promise-returning function

_Returns:_ [][function]

Convert Promise-returning to callback-last / error-first contract

$3

- fn: [][function] regular synchronous function

_Returns:_ [][function] with contract: callback-last / error-first

Convert sync function to callback-last / error-first contract

$3

- promise: [][promise]
- callback: [][function]

Convert Promise to callback-last

$3

- fn: [][function] callback-last function

_Returns:_ [][function] Promise-returning function

Convert async function to Promise-returning function

$3

- fn: [][function] regular synchronous function

_Returns:_ [][function] Promise-returning function

Convert sync function to Promise object

$3

- items: [][array] incoming
- fn: [][function] to be executed for each value in the array
- current: current element being processed in the array
- callback: [][function]
- err: [][error]|[][null]
- value:
- done: [][function] on done
- err: [][error]|[][null]
- result: [][array]

Asynchronous map (iterate parallel)

$3

- items: [][array] incoming
- fn: [][function] to be executed for each value in the array
- value: item from items array
- callback: [][function]
- err: [][error]|[][null]
- accepted: [][boolean]
- done: [][function] on done
- err: [][error]|[][null]
- result: [][array]

Asynchrous filter (iterate parallel)

_Example:_

`js
metasync.filter(
['data', 'to', 'filter'],
(item, callback) => callback(item.length > 2),
(err, result) => console.dir(result)
);
`

$3

- items: [][array] incoming
- fn: [][function] to be executed for each value in array
- previous: value previously returned in the last iteration
- current: current element being processed in the array
- callback: [][function] callback for returning value back to
reduce function
- err: [][error]|[][null]
- data: resulting value
- counter: [][number] index of the current element being processed
in array
- items: [][array] the array reduce was called upon
- done: [][function] on done
- err: [][error]|[][null]
- result: [][array]
- initial: optional value to be used as first argument in first
iteration

Asynchronous reduce

$3

- items: [][array] incoming
- fn: [][function] to be executed for each value in array
- previous: value previously returned in the last iteration
- current: current element being processed in the array
- callback: [][function] callback for returning value back to
reduce function
- err: [][error]|[][null]
- data: resulting value
- counter: [][number] index of the current element being processed
in array
- items: [][array] the array reduce was called upon
- done: [][function] on done
- err: [][error]|[][null]
- result: [][array]
- initial: optional value to be used as first argument in first
iteration

Asynchronous reduceRight

$3

- items: [][array] incoming
- fn: [][function]
- value: item from items array
- callback: [][function]
- err: [][error]|[][null]
- done: [][function] on done
- err: [][error]|[][null]
- items: [][array]

Asynchronous each (iterate in parallel)

_Example:_

`js
metasync.each(
['a', 'b', 'c'],
(item, callback) => {
console.dir({ each: item });
callback();
},
(err, data) => console.dir('each done')
);
`

$3

- items: [][array] incoming
- fn: [][function]
- value: item from items array
- callback: [][function]
- err: [][error]|[][null]
- done: [][function] on done
- err: [][error]|[][null]
- items: [][array]

Asynchronous series

_Example:_

`js
metasync.series(
['a', 'b', 'c'],
(item, callback) => {
console.dir({ series: item });
callback();
},
(err, data) => {
console.dir('series done');
}
);
`

$3

- items: [][array] incoming
- fn: [][function]
- value: item from items array
- callback: [][function]
- err: [][error]|[][null]
- accepted: [][boolean]
- done: [][function] on done
- err: [][error]|[][null]
- result:

Asynchronous find (iterate in series)

_Example:_

`js
metasync.find(
[1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16],
(item, callback) => callback(null, item % 3 === 0 && item % 5 === 0),
(err, result) => {
console.dir(result);
}
);
`

$3

- items: [][array] incoming
- fn: [][function]
- value: item from items array
- callback: [][function]
- err: [][error]|[][null]
- accepted: [][boolean]
- done: [][function] on done
- err: [][error]|[][null]
- result: [][boolean]

Asynchronous every

$3

- items: [][array] incoming
- fn: [][function]
- value: item from items array
- callback: [][function]
- err: [][error]|[][null]
- accepted: [][boolean]
- done: [][function] on done
- err: [][error]|[][null]
- result: [][boolean]

Asynchronous some (iterate in series)

$3

- items: [][array] incoming dataset
- fn: [][function]
- item:
- index: [][number]
- options: [