promise streams

gistfile1.js

function traceurPromise() {
    console.log('STARTING TRACEUR ');
    return new Promise(function (resolve, reject) {
        gulp.src(es6files)
            .pipe(traceur(traceurOpts))
            .pipe(gulp.dest(distDirectory))
            .on('end', function () {
                console.log('ENDED TRACEUR ');
                resolve();
            });
    });
}