Asynchronous chain

asyncChain.js

function chain() {
  var queue = []
    , withoutContext = null

  function chainer(func) {
    queue.push(func)
    return chainer
  }
  chainer.run = function () {return run(queue)}

  function run(queue /*, ...*/) {
    if (queue.length === 0) return 
    var skipFirst = 1
      , params = slice(arguments, skipFirst)
      , restOfQueue = slice(queue, skipFirst)
      , func = queue[0]
    if (isAsync(func, params)) {
      func.apply(withoutContext, params.concat([doneCallback(restOfQueue)]))
    } else {
      var ret = func.apply(withoutContext, params)
      run(restOfQueue, ret)
    }
  }
  function isAsync(func, params) {return func.length > params.length}
  function slice(x, skipFromBeginning) {return [].slice.call(x, skipFromBeginning)}
  function doneCallback(queue) {return function (/*...*/) {run.apply(withoutContext, [queue].concat(slice(arguments)))}}
  return chainer
}

// Example
chain()
  (just([1,2,3,4,5,6]))
  (filter(even))
  (map(double))
  (delayTwoSeconds)  
  (print)
  .run()
  
// Details
function filter(func) {return function (arr) {return arr.filter(func)}}
function map(func)    {return function (arr) {return arr.map(func)}}
function just(x)      {return function () {return x}}

function even(x)   {return x%2==0}
function double(x) {return x*2}

function print(x) {console.log(x)}
function delayTwoSeconds(arr, done) {setTimeout(function () {done(arr)}, 2000)}