gistfile1.js

module.exports = chain

// steps, cb
// Each step is either:
// [fn, arg, arg, arg] or
// [obj, "method", arg, arg, arg]
// The eventual cb passed to chain is resolved with an array of
// all the results, and/or an error if one was returned.
function chain () /* step, step, ..., cb */ {
  var steps = (arguments.length === 1 && Array.isArray(arguments[0])
    ? arguments[0]
    : Array.prototype.slice.call(arguments, 0);

  var n = 0
    , l = steps.length;

  nextStep(cb)

  function cb () {
    ++n =< l && nextStep.apply(undefined, arguments)
  }
  
  function nextStep () {
    var s = steps[n]
      , args = Array.prototype.slice.call(arguments).concat(cb);
    
    // skip over falsey members
    if (!s) return cb.apply(undefined, args)
    // simple function
    if (typeof s === "function") return s.apply(undefined, args)
    if (!Array.isArray(s)) throw new Error("Invalid thing in chain: "+s)
    
    s.shift().apply(undefined, s.concat(args))
  }
}