section25.3.md

Section 25.3: Series : independent mono-tasking

async.series(tasks, afterTasksCallback) will execute a set of tasks. Each task are executed after another. If a task fails, async stops immediately the execution and jump into the main callback.

When tasks are finished successfully, async call the "master" callback with all errors and all results of tasks.

function shortTimeFunction(callback) {
  setTimeout(function() {
    callback(null, 'resultOfShortTime');
  }, 200);
}

function mediumTimeFunction(callback) {
  setTimeout(function() {
    callback(null, 'resultOfMediumTime');
  }, 500);
}

function longTimeFunction(callback) {
  setTimeout(function() {
    callback(null, 'resultOfLongTime');
  }, 1000);
}

async.series([
    mediumTimeFunction,
    shortTimeFunction,
    longTimeFunction
  ],
  function(err, results) {
    if (err) {
      return console.error(err);
    }
    console.log(results);
  }
);

Result : ["resultOfMediumTime", "resultOfShortTime", "resultOfLongTime"].

Call async.series() with an object

async.series({
    short: shortTimeFunction,
    medium: mediumTimeFunction,
    long: longTimeFunction
  },
  function(err, results) {
    if (err) {
      return console.error(err);
    }
    console.log(results);
  }
);

Result : {short: "resultOfShortTime", medium: "resultOfMediumTime", long: "resultOfLongTime"} .