npm install -D gulp browserify babelify @babel/core @babel/preset-env vinyl-source-stream vinyl-buffer gulp-uglify gulp-htmlmin cssnano gulp-postcss del

gulpfile.js

const gulp = require("gulp");
const browserify = require("browserify");
const source = require("vinyl-source-stream");
const buffer = require("vinyl-buffer");
const babelify = require("babelify");
const uglify = require("gulp-uglify");
const htmlmin = require("gulp-htmlmin");
const postcss = require("gulp-postcss");
const cssnano = require("cssnano");
const del = require("del");

const paths = {
	source: "./src",
	build: "./build"
};

function javascriptBuild() {
	return browserify({
		entries: [`${paths.source}/scripts/main.js`],
		transform: [babelify.configure({ presets: ["@babel/preset-env"] })]
	})
		.bundle()
		.pipe(source("bundle.js"))
		.pipe(buffer())
		.pipe(uglify())
		.pipe(gulp.dest(`${paths.build}/scripts`));
}

function htmlBuild() {
	return gulp
		.src(`${paths.source}/*.html`)
		.pipe(htmlmin())
		.pipe(gulp.dest(paths.build));
}

function cssBuild() {
	return gulp
		.src(`${paths.source}/styles/**/*.css`)
		.pipe(postcss([cssnano()]))
		.pipe(gulp.dest(`${paths.build}/styles`));
}

function cleanup() {
	return del([paths.build]);
}

// Run using gulp or gulp build
exports.default = exports.build = gulp.series(
	cleanup,
	gulp.parallel(javascriptBuild, htmlBuild, cssBuild)
);