How to get a directory size of the current Total.js application?

const Exec = require('child_process').exec;

NEWOPERATION('directorysize', function(error, value, callback) {
    Exec('du -sk ' + (value === EMPTYOBJECT ? F.path.root() : value), function(err, response) {
        err && error.push(err);
        var size = null;
         var match = response.trim().match(/^[\d\.\,]+/);
         match && (size = match.toString().trim().parseInt2() * 1024);
        callback(size);
    });
});

OPERATION('directorysize', function(err, response) {
    console.log(err, response.filesize());
});

// Or another directory e.g. "databases"
OPERATION('directorysize', F.path.databases(), function(err, response) {
    console.log(err, response.filesize());
});