control flow library, from mixu's node book

seriesLib.js

function series (callbacks, last) {
  var results = [];
  function next () {
    var callback = callbacks.shift();

    if(callback) {
      callback(function() {
        results.push(Array.prototype.slice.call(arguments));
        next();
      });
    } else {
      last(results);
    }
  }
  next();
}

// Example task
function async (arg, callback) {
  var delay = Math.floor(Math.random() * 5 + 1) * 100;
  console.log('async with \''+arg+'\', return in '+delay+' ms');
  setTimeout(function() { callback(arg * 2); }, delay);
}

function final(results) { console.log('Done', results); } 

series([
  function(next) { async(1, next); },
  function(next) { async(2, next); },
  function(next) { async(3, next); },
  function(next) { async(4, next); },
  function(next) { async(5, next); },
  function(next) { async(6, next); }
], final);