Gulp

gulpfile.js

const gulp = require('gulp');

const minify = require('gulp-minify');
const minifyCSS = require('gulp-minify-css');
const rename = require('gulp-rename');
const concat = require('gulp-concat');

gulp.task('styles', () => {
	gulp.src('source/css/**/*.css')
		.pipe(minifyCSS())
		.pipe(rename({ suffix: '.min' }))
		.pipe(gulp.dest('dist/css'))
});

gulp.task('scripts', () => {
	gulp.src(['source/js/**/*.js'])
		.pipe(concat('all.js'))
		.pipe(minify({
			ext: {
				min: '.min.js'
			},
			noSource: true
		}))
		.pipe(gulp.dest('dist/js'))
});

gulp.task('watch', () => {
	gulp.watch('source/css/**/*.css', ['styles']);
	gulp.watch('source/js/**/*.js', ['scripts']);
});

gulp.task('default', ['styles', 'scripts', 'watch']);

package.json

{
  "name": "project",
  "version": "1.0.0",
  "description": "",
  "main": "index.js",
  "scripts": {
    "test": "echo \"Error: no test specified\" && exit 1"
  },
  "author": "",
  "license": "ISC",
  "devDependencies": {
    "gulp": "^3.9.1",
    "gulp-concat": "^2.6.1",
    "gulp-minify": "^2.1.0",
    "gulp-minify-css": "^1.2.4",
    "gulp-rename": "^1.2.2"
  }
}