Gulp 4 tasks for PUG+SCSS+JS and imagemin

gulpfile.js

const
    gulp                = require('gulp'),
    pug                 = require('gulp-pug'),    
    sourcemaps          = require('gulp-sourcemaps'),
    concat              = require('gulp-concat'),
      
    cleanCSS            = require('gulp-clean-css'),
    mmq                 = require('gulp-merge-media-queries'),

    babel               = require('gulp-babel'),
    uglify              = require('gulp-uglify'),

    cache               = require('gulp-cache'),
    imagemin            = require('gulp-imagemin'),
    imageminOptipng     = require('imagemin-optipng'),
    imageminZopfli      = require('imagemin-zopfli'),
    imageminMozjpeg     = require('imagemin-mozjpeg');

gulp.task('pug', function buildHTML() {
    return gulp.src('build/pug/pages/*.pug')
        .pipe(pug({
            pretty: true
        }))
        .pipe(gulp.dest('.'))
})

gulp.task('sass', () => {
    return gulp.src(['global.css', '1.css', '2.css'].map(file => `build/css/${file}`))
        .pipe(sourcemaps.init())
        .pipe(concat('style.min.css'))
        .pipe(mmq({
            log: true
        }))
        .pipe(cleanCSS())
        .pipe(sourcemaps.write('.'))
        .pipe(gulp.dest('css'))
})

gulp.task('scripts', () => {
    return gulp.src('build/js/*.js')
        .pipe(sourcemaps.init())
        .pipe(babel({
            presets: ['@babel/preset-env']
        }))
        .pipe(concat('scripts.min.js'))
        .pipe(uglify())
        .pipe(sourcemaps.write('.'))
        .pipe(gulp.dest('js'))
})

gulp.task('assembly', () => {
    gulp.watch('build/pug/pages/*.pug', gulp.series('pug'))
    gulp.watch('build/css/*.css', gulp.series('sass'))
    gulp.watch('build/js/*.js', gulp.series('scripts'))
})

gulp.task('watch', gulp.series(gulp.parallel('pug', 'sass', 'scripts'), 'assembly'))

gulp.task('imagemin', () => {
  return gulp.src('build/src/**/*.{png,jpg}')
        .pipe(cache(imagemin([
            imageminOptipng({
                optimizationLevel: 5
            }),
            imageminZopfli({
                more: true
            }),
            imagemin.jpegtran({
                progressive: true
            }),
            imageminMozjpeg({
                quality: 80
            })
        ])))
        .pipe(gulp.dest('src/new'))
})