asynckit

Minimal async jobs utility library, with streams support.

AsyncKit provides harness for parallel and serial iterators over list of items represented by arrays or objects. Optionally it accepts abort function (should be synchronously return by iterator for each item), and terminates left over jobs upon an error event. For specific iteration order built-in (ascending and descending) and custom sort helpers also supported, via asynckit.serialOrdered method.

It ensures async operations to keep behavior more stable and prevent Maximum call stack size exceeded errors, from sync iterators.

compression

size

Install

$ npm install --save asynckit

Examples

Parallel Jobs

Runs iterator over provided array in parallel. Stores output in the result array, on the matching positions. In unlikely event of an error from one of the jobs, will terminate rest of the active jobs (if abort function is provided) and return error along with salvaged data to the main callback function.

Input Array

var parallel = require('asynckit').parallel
  , assert   = require('assert')
  ;

var source         = [ 1, 1, 4, 16, 64, 32, 8, 2 ]
  , expectedResult = [ 2, 2, 8, 32, 128, 64, 16, 4 ]
  , expectedTarget = [ 1, 1, 2, 4, 8, 16, 32, 64 ]
  , target         = []
  ;

parallel(source, asyncJob, function(err, result)
{
  assert.deepEqual(result, expectedResult);
  assert.deepEqual(target, expectedTarget);
});

// async job accepts one element from the array
// and a callback function
function asyncJob(item, cb)
{
  // different delays (in ms) per item
  var delay = item * 25;

  // pretend different jobs take different time to finish
  // and not in consequential order
  var timeoutId = setTimeout(function() {
    target.push(item);
    cb(null, item * 2);
  }, delay);

  // allow to cancel "leftover" jobs upon error
  // return function, invoking of which will abort this job
  return clearTimeout.bind(null, timeoutId);
}

More examples could be found in test/test-parallel-array.js.

Input Object

Also it supports named jobs, listed via object.

var parallel = require('asynckit/parallel')
  , assert   = require('assert')
  ;

var source         = { first: 1, one: 1, four: 4, sixteen: 16, sixtyFour: 64, thirtyTwo: 32, eight: 8, two: 2 }
  , expectedResult = { first: 2, one: 2, four: 8, sixteen: 32, sixtyFour: 128, thirtyTwo: 64, eight: 16, two: 4 }
  , expectedTarget = [ 1, 1, 2, 4, 8, 16, 32, 64 ]
  , expectedKeys   = [ 'first', 'one', 'two', 'four', 'eight', 'sixteen', 'thirtyTwo', 'sixtyFour' ]
  , target         = []
  , keys           = []
  ;

parallel(source, asyncJob, function(err, result)
{
  assert.deepEqual(result, expectedResult);
  assert.deepEqual(target, expectedTarget);
  assert.deepEqual(keys, expectedKeys);
});

// supports full value, key, callback (shortcut) interface
function asyncJob(item, key, cb)
{
  // different delays (in ms) per item
  var delay = item * 25;

  // pretend different jobs take different time to finish
  // and not in consequential order
  var timeoutId = setTimeout(function() {
    keys.push(key);
    target.push(item);
    cb(null, item * 2);
  }, delay);

  // allow to cancel "leftover" jobs upon error
  // return function, invoking of which will abort this job
  return clearTimeout.bind(null, timeoutId);
}

More examples could be found in test/test-parallel-object.js.

Serial Jobs

Runs iterator over provided array sequentially. Stores output in the result array, on the matching positions. In unlikely event of an error from one of the jobs, will not proceed to the rest of the items in the list and return error along with salvaged data to the main callback function.

Input Array

var serial = require('asynckit/serial')
  , assert = require('assert')
  ;

var source         = [ 1, 1, 4, 16, 64, 32, 8, 2 ]
  , expectedResult = [ 2, 2, 8, 32, 128, 64, 16, 4 ]
  , expectedTarget = [ 0, 1, 2, 3, 4, 5, 6, 7 ]
  , target         = []
  ;

serial(source, asyncJob, function(err, result)
{
  assert.deepEqual(result, expectedResult);
  assert.deepEqual(target, expectedTarget);
});

// extended interface (item, key, callback)
// also supported for arrays
function asyncJob(item, key, cb)
{
  target.push(key);

  // it will be automatically made async
  // even it iterator "returns" in the same event loop
  cb(null, item * 2);
}

More examples could be found in test/test-serial-array.js.

Input Object

Also it supports named jobs, listed via object.

var serial = require('asynckit').serial
  , assert = require('assert')
  ;

var source         = [ 1, 1, 4, 16, 64, 32, 8, 2 ]
  , expectedResult = [ 2, 2, 8, 32, 128, 64, 16, 4 ]
  , expectedTarget = [ 0, 1, 2, 3, 4, 5, 6, 7 ]
  , target         = []
  ;

var source         = { first: 1, one: 1, four: 4, sixteen: 16, sixtyFour: 64, thirtyTwo: 32, eight: 8, two: 2 }
  , expectedResult = { first: 2, one: 2, four: 8, sixteen: 32, sixtyFour: 128, thirtyTwo: 64, eight: 16, two: 4 }
  , expectedTarget = [ 1, 1, 4, 16, 64, 32, 8, 2 ]
  , target         = []
  ;


serial(source, asyncJob, function(err, result)
{
  assert.deepEqual(result, expectedResult);
  assert.deepEqual(target, expectedTarget);
});

// shortcut interface (item, callback)
// works for object as well as for the arrays
function asyncJob(item, cb)
{
  target.push(item);

  // it will be automatically made async
  // even it iterator "returns" in the same event loop
  cb(null, item * 2);
}

More examples could be found in test/test-serial-object.js.

Note: Since object is an unordered collection of properties, it may produce unexpected results with sequential iterations. Whenever order of the jobs' execution is important please use serialOrdered method.