gulpfile.js

var gulp = require('gulp'),
  folderIndex = require('gulp-folder-index'),
  browserSync = require('browser-sync').create(),
  source = './docs/',
  dest = './docs/'

function html() {
  return gulp.src(dest + '**/*.html')
}

function js() {
  return gulp.src(dest + '**/*.js')
}

function styles() {
  return gulp.src(dest + '**/*.css')
}

function slides() {
  return gulp
    .src(source + 'slides/**/*.md')
    .pipe(
      folderIndex({
        extension: '.md',
        filename: 'index.json'
      })
    )
    .pipe(gulp.dest(source + 'slides'))
}

function watch() {
  gulp.watch(source + 'js/**/*.js', js).on('change', browserSync.reload)
  gulp.watch(source + 'css/**/*.css', styles).on('change', browserSync.reload)
  gulp.watch(source + 'index.html', html).on('change', browserSync.reload)
  gulp.watch(source + 'slides/**/*.md', slides).on('change', browserSync.reload)
}

function server() {
  browserSync.init({
    notify: false,
    server: {
      baseDir: source
    }
  })

  gulp.watch(source + 'css/**/*.css', styles).on('change', browserSync.reload)
  gulp.watch(source + 'index.html', html).on('change', browserSync.reload)
  gulp.watch(source + 'slides/**/*.md', slides).on('change', browserSync.reload)
}

var build = gulp.series(gulp.parallel(slides, js, styles, html), server, watch)

gulp.task('default', build)