code: function buildScript(file, dest) {
      var bundler = browserify({
              entries: [file],
              cache: {},
              packageCache: {}
          }, watchify.args),
          srcFile = file.substring(file.lastIndexOf('/')+1);
  
      if ( environment !== 'production' ) {
          bundler = watchify(bundler);
          bundler.on('update', function() {
              rebundle();
          });
      }
  
      function rebundle() {
          gutil.log('Running rebundle');
          return bundler.bundle()
              .on('error', gutil.log.bind(gutil, 'Browserify Error'))
              .pipe( source(srcFile) )
              .pipe( buffer() )
              .pipe( productionOnly(uglify) )
              .pipe( gulp.dest(dest) )
              .pipe( developmentOnly( browserSync.reload, {stream:true} ) );
      }
  
      return rebundle();
  }
docs: Based on: http://blog.avisi.nl/2014/04/25/how-to-keep-a-fast-build-with-browserify-and-reactjs/