gulpfile.js

const babel = require('gulp-babel');
const chmod = require('gulp-chmod');
const eslint = require('gulp-eslint');
const gulp = require('gulp');
const gulpIf = require('gulp-if');

gulp.task('scripts', done => {
    gulp.src('./lib/src/**/*.js')
        .pipe(babel({
            presets: ['es2015']
        }))
        .pipe(gulp.dest('dist'));

    gulp.src('./lib/src/**/*.json')
        .pipe(gulp.dest('dist'));

    gulp.src('./lib/*.js')
        .pipe(babel())
        .pipe(chmod(0o755))
        .pipe(gulp.dest('bin'));

    done();
});

gulp.task('lint', () => {
    const isFixed = file => file.eslint != null && file.eslint.fixed;

    return gulp.src('./lib/**/*.js')
        .pipe(
            eslint({
                fix: true,
                envs: [
                    'node'
                ]
            })
        )
        .pipe(eslint.format())
        .pipe(gulpIf(isFixed, gulp.dest('./lib/')));
});

gulp.task('watch', () => gulp.watch('./lib/**/*.js', gulp.series(['lint', 'scripts'])));

gulp.task('build', gulp.series(['lint', 'scripts']));
gulp.task('default', gulp.series(['build', 'watch']));