text: # asynckit [![NPM Module](https://img.shields.io/npm/v/asynckit.svg?style=flat)](https://www.npmjs.com/package/asynckit)
  
  Minimal async jobs utility library, with streams support.
  
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  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 |
  | :----------------- | -------: |
  | asynckit.js        | 12.34 kB |
  | asynckit.min.js    |  4.11 kB |
  | asynckit.min.js.gz |  1.47 kB |
  
  
  ## Install
  
  ```sh
  $ 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
  
  ```javascript
  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](test/test-parallel-array.js).
  
  #### Input Object
  
  Also it supports named jobs, listed via object.
  
  ```javascript
  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](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
  
  ```javascript
  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](test/test-serial-array.js).
  
  #### Input Object
  
  Also it supports named jobs, listed via object.
  
  ```javascript
  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](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._
  
  ### Ordered Serial Iterations
  
  TBD
  
  For example [compare-property](compare-property) package.
  
  ### Streaming interface
  
  TBD
  
  ## Want to Know More?
  
  More examples can be found in [test folder](test/).
  
  Or open an [issue](https://github.com/alexindigo/asynckit/issues) with questions and/or suggestions.
  
  ## License
  
  AsyncKit is licensed under the MIT license.
  