npm + gulp for scss and js minifying

gulpfile.js

var gulp = require('gulp');
var sass = require('gulp-sass');
// var sourcemaps = require('gulp-sourcemaps');
var postcss = require('gulp-postcss');
var babel = require('gulp-babel');
var rename = require('gulp-rename');
var uglify = require('gulp-uglify');

function style(path, dest) {
	return (
		gulp.src(path)
			// .pipe(sourcemaps.init())
			.pipe(sass({ outputStyle: 'compressed' }))
			.on("error", sass.logError)
			.pipe(postcss([ require('autoprefixer') ]))
			// .pipe(sourcemaps.write())
			.pipe(rename((path) => {
				path.extname = '.min.css'
			}))
			.pipe(gulp.dest(dest))
	);
}

function script(path, dest) {
	return (
		gulp.src(path)
			.pipe(babel({ presets: ['@babel/env']}))
			.pipe(uglify())
			.pipe(rename((path) => {
				path.extname = '.min.js'
			}))
			.pipe(gulp.dest(dest))
	);
}

exports.style = style;
exports.script = script;

function watch() {
	gulp.watch('src/scss/*.scss', () => { return style('src/scss/*.scss', 'public/css') })
	gulp.watch('src/js/*.js', () => { return script('src/js/*.js', '/public/js') });
}

exports.watch = watch

package.json

{
	"name": "",
	"version": "1.0.0",
	"description": "",
	"main": "public/index.php",
	"scripts": {
		"watch-sources": "gulp watch"
	},
	"author": "Dion Purushotham <mail@dion.codes>",
	"license": "ISC",
	"devDependencies": {
		"@babel/core": "^7.7.4",
		"@babel/preset-env": "^7.7.4",
		"babel-preset-minify": "^0.5.1",
		"gulp": "^4.0.2",
		"gulp-autoprefixer": "^7.0.1",
		"gulp-babel": "^8.0.0",
		"gulp-postcss": "^8.0.0",
		"gulp-rename": "^2.0.0",
		"gulp-sass": "^4.0.0",
		"gulp-uglify": "^3.0.2"
	},
	"dependencies": {}
}

setup.md

1. copy both files to the project's main directory (if no npm is existing yet, otherwise require dev dependencies in existing package.json)
2. adjust the paths in gulpfile.js to match your source and destination folders (duplicate calls in watch() method for multiple directories)
3. watch files with gulp watch