Use serialized or parallelized callback in nodejs

serialized_parallelized_callback.js

// prints text and waits one second
function doSomethingAsync(callback) {
    console.log('doSomethingAsync: Wait for one second.');
    setTimeout(function() { callback(); }, 1000);
}
 
// prints text and waits half a second
function doSomethingElseAsync(callback) {
    console.log('doSomethingElseAsync: Wait for half a sec.');
    setTimeout(function() { callback(); }, 500);
}
 
// prints text and waits two seconds
function moreAsync(callback) {
    console.log('moreAsync: Wait for two seconds.');
    setTimeout(function() { callback(); }, 2000);
}
 
// prints text and waits a second and a half
function evenMoreAsync(callback) {
    console.log('evenMoreAsync: Wait for a second and a half.');
    setTimeout(function() { callback(); }, 1500);
}

// prints text
function finish() { console.log('Finished.'); }


// executes the callbacks one after another
function series() {
    var callbackSeries = [doSomethingAsync, doSomethingElseAsync, 
                          moreAsync, evenMoreAsync];
 
    function next() {
        var callback = callbackSeries.shift();
        if (callback) {
            callback(next);
        }
        else {
            finish();
        }
    }
    next();
};
 
// run the example
series();


// execute callbacks in parallel
function parallel() {
    var callbacksParallel = [doSomethingAsync, doSomethingElseAsync, 
                             moreAsync, evenMoreAsync];
    var executionCounter = 0;
    callbacksParallel.forEach(function(callback, index) {
        callback(function() {
            executionCounter++;
            if(executionCounter == callbacksParallel.length) {
                finish();
            }
        });
    });
}
 
// run the example
parallel();