http://www.slideshare.net/iamhjoo/flow-control-in-nodejs-12947355

asyncmap.js

function asyncMap( list, fn, cb_ ) {
  var n = list.length
    , result = []
    , errState = null;
    
  function cb (er, data) {
    if (errState) return;
    if (er) return cb_(errState = er);
    results.push(data);
    if (--n === 0) // 모든 리스트 처리 완료시
      return cb_(null, results);
  }
  
  // action code
  list.forEach(function (l) {
    fn(l, cb);
  });
}

function asyncMapOrder( list, fn, cb_ ) {
  var n = list.length
    , result = []
    , errState = null;
  
  function cbGen (i) {
    return function cb (er, data) {
      if (errState) return;
      if (er) return cb_(errState = er);
      results[i] = data;
      if (--n === 0) // 모든 리스트 처리 완료시
        return cb_(null, results);
    }    
  }
    
  // action code
  list.forEach(function (l, i) {
    fn(l, cbGen(i));
  });
}