text: const gulp = require('gulp4');
  const devServer = require('gulp-develop-server');
  const notifier = require('node-notifier');
  
  const files = [
    './src/**/*.js'
  ];
  
  gulp.task('server:start', done => {
    devServer.listen({ path: './src/index.js' }, err => err && console.error(err));
    done();
  });
  
  gulp.task('server:restart', done => {
    devServer.restart(err => {
      err && console.error(err);
    });
    notifier.notify({
      title: 'Notify',
      sound: true,
      message: 'Server restart successfully.'
    });
    done();
  });
  
  gulp.task('watch', done => {
    gulp.watch(files).on('change', gulp.series('server:restart'));
    done();
  });
  
  gulp.task('default', gulp.series('server:start', 'watch'));
  