Edit in JSFiddle

var data = [];
for (var i = 0; i < 100; i = i + 5) {
    data.push(i);
}
$('#output').append('Our Inital Array<br/>');
$('#output').append('====================<br/>');
for (var i = 0; i < 100; i = i + 5) {
    $('#output').append(i + "<br/>");
}
$('#output').append('====================' + '<br/>');
$('#output').append('Lets start Parallel Processing' + '<br/>');
async.each(data, processData, function (err) {
    if (err) {
        $('#output').append('OOPS! How is this possible?' + "<br/>");
    }
    $('#output').append('Parallel Processing Done<br/>');
    $('#output').append('====================' + '<br/>');
    $('#output').append('Lets Start Same Operation In Series');
    async.eachSeries(data, processData, function (err) {
        if (err) {
            $('#output').append('OOPS! How is this possible?' + "<br/>");
        }
        $('#output').append('Series Processing Done<br/>');
        $('#output').append('====================' + '<br/>');
        $('#output').append('Lets Start Same Operation In Series But With 5 at time');
        async.eachLimit(data, 5, processData, function (err) {
            if (err) {
                $('#output').append('OOPS! How is this possible?' + "<br/>");
            }
            $('#output').append('Series Processing Done<br/>');
            $('#output').append('====================' + '<br/>');
        });
    });
});

function processData(item, callback) {
    //we are just diving the number by 5
    //but we can actually do a very long process here 
    setTimeout(function () {
        var date = new Date();
        $('#output').append((item / 5) + ' Finished At ' + date.getHours() + ":" + +date.getMinutes() + ":" + +date.getSeconds() + '<br/>');
        callback(null); //no error
        //incase of error pass the error in callback function 
    }, 1000);
}