contra

Asynchronous flow control with a _ taste to it

λ aims to stay small and simple, while powerful. Inspired by async and lodash. Methods are implemented individually and not as part of a whole. That design helps when considering to export functions individually. If you need all the methods in async, then stick with it. Otherwise, you might want to check λ out!

Quick Links

• CHANGELOG
• Comparison with async
• Browser Support
• License

API

Flow Control

• λ.waterfall
• λ.series
• λ.concurrent

Functional

• λ.each
• λ.each.series
• λ.map
• λ.map.series
• λ.filter
• λ.filter.series

Uncategorized

• λ.queue
• λ.emitter
• λ.apply

Install

Install using npm or bower. Or get the source code and embed that in a <script> tag.

npm i contra --save

bower i contra --save

You can use it as a Common.JS module, or embed it directly in your HTML.

var λ = require('contra');

<script src='contra.js'></script>

API

These are the asynchronous flow control methods provided by λ.

λ.waterfall(tasks[, done])

Executes tasks in series. Each step receives the arguments from the previous step.

• tasks Array of functions with the (...results, next) signature
• done Optional function with the (err, ...results) signature

λ.waterfall([
  function (next) {
    next(null, 'params for', 'next', 'step');
  },
  function (a, b, c, next) {
    console.log(b);
    // <- 'next'
    next(null, 'ok', 'done');
  }
], function (err, ok, result) {
  console.log(result);
  // <- 'done'
});

λ.series(tasks[, done])

Executes tasks in series. done gets all the results. Results get passed as an array or hash to an optional done callback. Task order is preserved in results.

• tasks Collection of functions with the (next) signature. Can be an array or an object
• done Optional function with the (err, results) signature

λ.series([
  function (next) {
    setTimeout(function () {
      next(null, 'boom');
    }, 1000);
  },
  function (next) {
    next(null, 'foo');
  }
], function (err, results) {
  console.log(results);
  // <- ['boom', 'foo']
});

Using objects

λ.series({
  first: function (next) {
    setTimeout(function () {
      next(null, 'boom');
    }, 1000);
  },
  second: function (next) {
    next(null, 'foo');
  }
}, function (err, results) {
  console.log(results);
  // <- { first: 'boom', second: 'foo' }
});

λ.concurrent(tasks[, done])

Executes tasks concurrently. Results get passed as an array or hash to an optional done callback. Task order is preserved in results.

• tasks Collection of functions with the (cb) signature. Can be an array or an object
• done Optional function with the (err, results) signature

λ.concurrent([
  function (cb) {
    setTimeout(function () {
      cb(null, 'boom');
    }, 1000);
  },
  function (cb) {
    cb(null, 'foo');
  }
], function (err, results) {
  console.log(results);
  // <- ['boom', 'foo']
});

Using objects

λ.concurrent({
  first: function (cb) {
    setTimeout(function () {
      cb(null, 'boom');
    }, 1000);
  },
  second: function (cb) {
    cb(null, 'foo');
  }
}, function (err, results) {
  console.log(results);
  // <- { first: 'boom', second: 'foo' }
});

λ.each(items, iterator[, done])

Applies an iterator to each element in the collection concurrently.

• items Collection of items. Can be an array or an object
• iterator(item, cb) Function to execute on each item
  • item The current item
  • cb Needs to be called when processing for current item is done
• done Optional function with the (err) signature

λ.each({ thing: 900, another: 23 }, function (item, cb) {
  setTimeout(function () {
    console.log(item);
    cb();
  }, item);
});
// <- 23
// <- 900

λ.each.series(items, iterator[, done])

Same as λ.each(items, iterator[, done]), but in series instead of concurrently.

λ.map(items, iterator[, done])

Applies an iterator to each element in the collection concurrently. Produces an object with the transformation results. Task order is preserved in the results.

• items Collection of items. Can be an array or an object
• iterator(item, cb) Function to execute on each item
  • item The current item
  • cb Needs to be called when processing for current item is done
• done Optional function with the (err, results) signature

λ.map({ thing: 900, another: 23 }, function (item, cb) {
  setTimeout(function () {
    cb(null, item * 2);
  }, item);
}, function (err, results) {
  console.log(results);
  <- { thing: 1800, another: 46 }
});

λ.map.series(items, iterator[, done])

Same as λ.map(items, iterator[, done]), but in series instead of concurrently.

λ.filter(items, iterator[, done])

Applies an iterator to each element in the collection concurrently. Produces an object with the filtered results. Task order is preserved in results.

• items Collection of items. Can be an array or an object
• iterator(item, cb) Function to execute on each item
  • item The current item
  • cb Needs to be called when processing for current item is done
    • err An optional error which will short-circuit the filtering process, calling done
    • keep Truthy will keep the item. Falsy will remove it in the results
• done Optional function with the (err, results) signature

λ.filter({ thing: 900, another: 23, foo: 69 }, function (item, cb) {
  setTimeout(function () {
    cb(null, item % 23 === 0);
  }, item);
}, function (err, results) {
  console.log(results);
  <- { another: 23, foo: 69 }
});

λ.filter.series(items, iterator[, done])

Same as λ.filter(items, iterator[, done]), but in series instead of concurrently.

λ.queue(worker[, concurrency=1])

Used to create a job queue.

• worker(job, done) Function to process jobs in the queue
  • job The current job
  • done Needs to be called when processing for current job is done
• concurrency Optional concurrency level, defaults to 1 (serial)

Returns a queue you can push or unshift jobs to. You can pause and resume the queue by hand.

• push(job[, done]) Array of jobs or an individual job object. Enqueue those jobs, resume processing. Optional callback to run when each job is completed
• unshift(job) Array of jobs or an individual job object. Add jobs to the top of the queue, resume processing. Optional callback to run when each job is completed
• length Property. Jobs that haven't started processing yet
• pause Stop processing jobs. Those already being processed will run to completion
• resume Start processing jobs again

var q = λ.queue(worker);

function worker (job, done) {
  console.log(job);
  done(null);
}

q.push('job', function () {
  console.log('this job is done!');
});

q.push(['some', 'more'], function () {
  console.log('one of these jobs is done!');
});

// <- 'job'
// <- 'some'
// <- 'more'

λ.emitter(thing)

Augments thing with on and emit methods.

• thing Writable JavaScript object
• emit(type, ...arguments) Emits an event of type type, passing arguments
• on(type, fn) Registers an event listener fn, of type type

var thing = { foo: 'bar' };

λ.emitter(thing);

thing.on('something', function (level) {
  console.log('something level ' + level);
});

thing.emit('something', 4);
// <- 'something level 4'

Returns thing.

Events of type error have a special behavior. λ.emitter will throw if there are no error listeners when an error event is emitted.

var thing = { foo: 'bar' };

λ.emitter(thing);

thing.emit('error', 'foo');
<- throws 'foo'

If an 'error' listener is registered, then it'll work just like any other event type.

var thing = { foo: 'bar' };

λ.emitter(thing);

thing.on('error', function (err) {
  console.log(err);
});

thing.emit('error', 'foo');
<- 'foo'

λ.apply(fn, ...arguments)

Returns a function bound with some arguments and a next callback.

λ.apply(fn, 1, 3, 5);
// <- function (next) { fn(1, 3, 5, next); }

Comparison with async

async	λ
Aimed at Noders	Tailored for browsers
Arrays for some, collections for others	Collections for everyone!
parallel	concurrent
mapSeries	map.series
More comprehensive	More focused
~29.6k (minified, uncompressed)	~2.6k (minified, uncompressed)

λ isn't meant to be a replacement for async. It aims to provide a more focused library, and a bit more consistency.

Browser Support

If you need support for legacy browsers, you'll need to include contra.shim.js as well.

• IE < 10
• Safari < 6
• Opera < 16

require('contra/shim');
var λ = require('contra');

<script src='contra.shim.js'></script>
<script src='contra.js'></script>

The shim currently clocks around ~700B minified.

License

MIT