It's easy to use: Gulp

gulpfile.js

let gulp = require('gulp');
let clean = require('gulp-clean');
let concat = require('gulp-concat');
let replace = require('gulp-replace');
let minifyCSS = require('gulp-clean-css');
let uglify = require('gulp-uglify-es').default;
let htmlmin = require('gulp-htmlmin');
let autoprefixer = require('gulp-autoprefixer');
let merge = require('merge-stream');

// Location to our files
let globs = {
  dist: './dist',
  css: './src/css/*.css',
  js: './src/js/*.js',
  html: './src/*.html',
  images: './src/assets/**',
  fonts: './src/fonts/**'
};

// Step: 1 - This will delete the folder and re-create it
gulp.task('clean', gulp.series(function() {
  return gulp.src(globs.dist, {read: false})
    .pipe(clean());
}));

// Step: 2 - Just copy fonts/ folder
gulp.task('fonts', gulp.series('clean', function() {
  return gulp.src(globs.fonts)
      .pipe(gulp.dest(globs.dist + '/fonts'));
}));

// Step: 3 - CSS processing
gulp.task('styles', gulp.series('clean', function() {
  return gulp.src(globs.css)
    .pipe(concat('main.min.css'))
    .pipe(autoprefixer())
    .pipe(minifyCSS())
    .pipe(gulp.dest(globs.dist + '/css'));
}));

// Step: 4 - JS processing
gulp.task('js', gulp.series('clean', function() {
  return gulp.src(globs.js)
    .pipe(concat('app.min.js'))
    .pipe(uglify())
    .pipe(gulp.dest(globs.dist + '/js'));
}));

// Step: 5 - Image processing
gulp.task('assets', gulp.series('clean', function() {
  return gulp.src(globs.js)
    .pipe(imagemin())
    .pipe(gulp.dest(globs.dist + '/assets'));
}));

// Step: 6 - HTML processing
gulp.task('html', gulp.series('clean', function() {
  return gulp.src(globs.html)
    .pipe(replace(`<link rel="stylesheet" href="css/01-style1.css">`, ''))
    .pipe(replace(`<link rel="stylesheet" href="css/02-style2.css">`, ''))
    // Replace this with our one `main.min.css` file
    .pipe(replace(`<link rel="stylesheet" href="css/03-style3.css">`, '<link rel="stylesheet" href="css/main.min.css">'))

    .pipe(replace(`<script src="js/01-app1.js"></script>`, ''))
    .pipe(replace(`<script src="js/02-app2.js"></script>`, ''))
    .pipe(replace(`<script src="js/03-app3.js"></script>`, '<script src="js/app.min.js"></script>'))
    .pipe(htmlmin({
      collapseWhitespace: true,
      removeComments: true
    }))
    .pipe(gulp.dest('./dist'));
}));

// Step: 7 - Build the task
gulp.task('build', gulp.parallel('fonts', 'styles', 'js', 'assets', 'html'));
gulp.task('default', gulp.series('build'));