bluebird_example_1.js

//Earlier
var B = require('bluebird');
//Later

/**
 * Promise wrapper for fs.watch
 * @param path
 * @returns {*}
 */

function fsWatchAsync(path) {
    var deferred = B.defer();
    fs.watch(path, function (event, filename) {
        deferred.resolve(event, filename);
    });
    return deferred.promise;
}

/**
 * Promise wrapper for fs.exists
 * @param path
 * @returns {*}
 */

function fsExistsAsync(path) {
    var deferred = B.defer();
    fs.exists(path, function (exists) {
        deferred.resolve(exists);
    });
    return deferred.promise;
}


/**
* Watch a folder for a migration file, read it, run a function based on its
* contents then rename the file to a date dot json. 
*/
function migrationWatcher(children) {

    var migration_folder = path.join(__dirname, '/migrations/');
    var migration_filename = 'migration.json';
    var migration_path = path.join(migration_folder, migration_filename)


    fsWatchAsync(migration_folder)
        .then(function (event, filename) { //Wait for any file event in folder
            var results = [];
            if (filename === migration_filename) {
                results.push(fsExistsAsync(migration_path)); //Queue a check migration.js exists job
            }
            return B.all(results);
        })
        .filter(function (item) { //Only continue pipeline if file exists
            return item === true;
        })
        .then(function () {
            return fs.readFileAsync(migration_path); //Read file
        })
        .then(function (file) {
            var migration = JSON.parse(file); //Parse file
            var completed_migration = path.join(__dirname, '/migrations/', (new Date()).toJSON() + '.json'); //Rename migration.js to {date}.json

            processMigration(children, migration);
            return fs.renameAsync(migration_path, completed_migration);
        })
        .error(function () {
            console.error("[Migration] Couldnt move migration.json to a dated filename");
        });
}