async.map that works with sparse arrays

async-sparse-map.js

function asyncMap(sparseArr, factory, cb) {
  var completed = []
    , sparseLen = sparseArr.length
    , len = 0
    , ctr = 0
    , isDone = false
    , item
    , i;

  function done(err, good) {
    if (isDone) return;
    if (err) {
      isDone = true;
      return cb(err);
    }
    completed.push(good);
    item = sparseArr[i];
    if (++ctr === len) cb(null, completed);
  }

  function doOne(item) {
    process.nextTick(function () {
      factory(item, done);
    });
  }

  for (i = 0; i < sparseLen; i++) {
    item = sparseArr[i];
    if ('undefined' === typeof item) continue;
    len++;
    doOne(item);
  }
}