Elixir minify each file by folder with watch (not concat)

glupfile.js

var elixir = require('laravel-elixir');
var gulp = require('gulp');
var Task = elixir.Task;
var uglify = require('gulp-uglify');

elixir.extend('folder', function (folder, dest) {
  if (!dest) {
    dest = folder;
  }
  new Task('folder', function () {
      gulp.src('./resources/assets/' + folder + '/**/*.js')
        .pipe(uglify())
        .pipe(gulp.dest('public/' + dest + '/'));
    })
    .watch('./resources/assets/' + folder + '/**/*.js');
});

elixir(function (mix) {
  mix.folder('js/single_scripts/','js') //will copy each file in asset/js/single_scripts/ minified tp public/js
});