const fs = require('fs');
const path = require('path');

function filewalker(dir, done) {
    let results = [];

    fs.readdir(dir, function(err, list) {
        if (err) return done(err);

        var pending = list.length;

        if (!pending) return done(null, results);

        list.forEach(function(file) {
            file = path.resolve(dir, file);

            fs.stat(file, function(err, stat) {
                // If directory, execute a recursive call
                if (stat && stat.isDirectory()) {
                    // Add directory to array [comment if you need to remove the directories from the array]
                    results.push(file);

                    filewalker(file, function(err, res) {
                        results = results.concat(res);
                        if (!--pending) done(null, results);
                    });
                } else {
                    results.push(file);

                    if (!--pending) done(null, results);
                }
            });
        });
    });
};

const allData = filewalker("./data", function(err, data) {
    if (err) throw err;

    return data;
});



console.log(allData);