parallel-async.js

'use strict';

function asyncTask(data, callback) {
  process.setTimeout(function process() {
    return callback(null, 'processed ' + data);
  }, 100);
}

function doLotsOfStuff(callback) {
  var tasks = ['task1', 'task2', 'task3'];
  var results = [];
  tasks.forEach(function each(task) {
    asyncTask(task, function doneWithOneTask(error, result) {
      results.push(result);
      if (results.length === tasks.length) {
        callback(error, results);
      }
    });
  });
}

doLotsOfStuff(function done(error, results) {
  if (error) {
    throw error;
  }
  // do stuff with results
});