Gulp 4, Browserify transform for Babel & Watchify

gulpfile.js

const { watch, dest, series, parallel } = require('gulp');
const sourcemaps = require('gulp-sourcemaps');
const terser = require('gulp-terser-js');
const browserify = require('browserify');
const watchify = require('watchify');
const babelify = require('babelify');
const source = require('vinyl-source-stream');
const buffer = require('vinyl-buffer');

function Task() {
	return watchify(
		browserify({
			entries: [`./lib/index.js`],
			transform: [
				babelify.configure({ presets: ['@babel/preset-env'], plugins: ['@babel/plugin-transform-runtime', '@babel/plugin-transform-async-to-generator'] }),
			],
			standalone: 'std-test',
			debug: true,
		})
	)
		.bundle()
		.on('error', function(error) { console.error(error); this.emit('end'); })
		.pipe(source('bundle.js'))
		.pipe(buffer())
		.pipe(sourcemaps.init({ loadMaps: true }))
		.pipe(terser())
		.pipe(sourcemaps.write('.'))
		.pipe(dest('dist'));
}

function watchTask() {
	watch(['lib/**/*.js'], parallel(Task));
}

exports.default = series(clean, parallel(Task), watchTask);