Example using async library for paralel or series

async_sample.js

// Doc Async : https://caolan.github.io/async/v3/index.html
// Download : http://www.jsdelivr.com/projects/async

function task(item, callback) {
    setTimeout(function() {
        console.info(item + ' selesai');
        // null menandakan fungsi berhasil
        callback(null, item * 3);
        // jika gagal atau error, return dengan selain null
        // misal : callback('error','keterangan error');
    }, 100);    
}

var data = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11];

// data akan di kerjakan secara paralel 3-3-3..
async.mapLimit(data, 3, function(item, done) {
    task(item,done);
}, function(err, results) {
    // senua data telah selesai di proses
    console.log(results);
    // results =  [3, 6, 9, 12, 15, 18, 21, 24, 27, 30, 33]
});

// kalau ingin dikerjakan secara serries
async.mapSeries(data, function(item, done) {
    task(item,done);
}, function(err, results) {
    // senua data telah selesai di proses
    console.log(results);
});

// Menggunakan each
async.eachLimit(data, 4, function(item, done) {
    task(item,done);
}, function(err, results) {
    console.log('each', results);
    // results = undefined ( ini perbedaan dengan async.map )
});