gulpfile.js

const { series, src, dest } = require('gulp');
const useref = require('gulp-useref');
const cssnano = require('gulp-cssnano');
const gulpIf = require('gulp-if');
const babel = require('gulp-babel');
const del = require('del');
const terser = require('gulp-terser');

function clean(cb) {
	del.sync('deploy');
	cb();
}

function build() {
	return src('src/index.html')
		.pipe(useref())
		.pipe(
			gulpIf(
				'*.js',
				babel({
					presets: ['@babel/env']
				})
			)
		)
		.pipe(gulpIf('*.js', terser()))
		.pipe(gulpIf('*.css', cssnano()))
		.pipe(dest('deploy'));
}

function buildBackground() {
	return src(['src/js/background.js'])
		.pipe(
			gulpIf(
				'*.js',
				babel({
					presets: ['@babel/env']
				})
			)
		)
		.pipe(gulpIf('*.js', terser()))
		.pipe(dest('deploy/js'));
}

function copy(cb) {
	src('src/assets/**/*').pipe(dest('deploy/assets'));
	src('src/css/shared.css').pipe(dest('deploy/css'));
	src('src/manifest.json').pipe(dest('deploy'));
	src('src/options_page/**').pipe(dest('deploy/options_page'));
	cb();
}

exports.build = series(clean, build, buildBackground, copy);