gulpfile.js

const
    gulp                      = require('gulp'),
    sass                      = require('gulp-sass'),
    postcss                   = require('gulp-postcss'),
    autoprefixer              = require('gulp-autoprefixer'),
    minifyCss                 = require('gulp-clean-css'),
    babel                     = require('gulp-babel'),
    webpack                   = require('webpack-stream'),
    uglify                    = require('gulp-uglify'),
    concat                    = require('gulp-concat'),
    imagemin                  = require('gulp-imagemin'),

    src_folder                = './resources/',
    src_assets_folder         = src_folder + 'assets/',
    dist_folder               = './public/',
    dist_assets_folder        = dist_folder + 'assets/',
    node_modules_folder       = './node_modules/',
    dist_node_modules_folder  = dist_folder + 'node_modules/',

    node_dependencies         = Object.keys(require('./package.json').dependencies || {}).filter(dep => dep !== 'normalize.css');

gulp.task('sass', () => {
    return gulp.src([
        src_assets_folder + 'sass/**/*.sass'
    ])
        .pipe(sass())
        .pipe(postcss([
            require('postcss-import'),
        ]))
        .pipe(autoprefixer())
        .pipe(minifyCss())
        .pipe(gulp.dest(dist_assets_folder + 'css'));
});

gulp.task('js', () => {
    return gulp.src([ src_assets_folder + 'js/**/*.js' ], { since: gulp.lastRun('js') })
        .pipe(webpack({
            mode: 'production'
        }))
        .pipe(babel({
            presets: [ '@babel/env' ]
        }))
        .pipe(concat('all.js'))
        .pipe(uglify())
        .pipe(gulp.dest(dist_assets_folder + 'js'));
});

gulp.task('images', () => {
    return gulp.src([ src_assets_folder + 'images/**/*.+(png|jpg|jpeg|gif|svg|ico)' ], { since: gulp.lastRun('images') })
        .pipe(imagemin())
        .pipe(gulp.dest(dist_assets_folder + 'images'));
});

gulp.task('fonts', () => {
    return gulp.src([ src_assets_folder + 'fonts/**/*.+(eot|svg|ttf|woff|woff2)' ], { since: gulp.lastRun('fonts') })
        .pipe(gulp.dest(dist_assets_folder + 'fonts'));
});

gulp.task('vendor', () => {
    if (node_dependencies.length === 0) {
        return new Promise((resolve) => {
            console.log("No dependencies specified");
            resolve();
        });
    }

    return gulp.src(node_dependencies.map(dependency => node_modules_folder + dependency + '/**/*.*'), {
        base: node_modules_folder,
        since: gulp.lastRun('vendor')
    })
        .pipe(gulp.dest(dist_node_modules_folder));
});

gulp.task('build', gulp.series('sass', 'js', 'images', 'fonts', 'vendor'));

gulp.task('dev', gulp.series('sass', 'js'));

gulp.task('watch', () => {
    const watchImages = [
        src_assets_folder + 'images/**/*.+(png|jpg|jpeg|gif|svg|ico)',
    ];

    const watchFonts = [
        src_assets_folder + 'fonts/**/*.+(eot|svg|ttf|woff|woff2)',
    ];

    const watchVendor = [];

    node_dependencies.forEach(dependency => {
        watchVendor.push(node_modules_folder + dependency + '/**/*.*');
    });

    const watch = [
        src_assets_folder + 'sass/**/*.sass',
        src_assets_folder + 'js/**/*.js',
    ];

    gulp.watch(watch, gulp.series('dev'));
    gulp.watch(watchImages, gulp.series('images'));
    gulp.watch(watchFonts, gulp.series('fonts'));
    gulp.watch(watchVendor, gulp.series('vendor'));
});

gulp.task('default', gulp.series('build', 'watch'));