Using gulp as task manager on top of webpack and eleventy

gulpfile.js

const { series, watch, src, dest } = require("gulp");
const browserSync = require("browser-sync").create();
const del = require("delete");

// assets
const webpack = require("webpack");
const webpackConfig = require("./webpack.config.js");

// site generator
const exec = require("child_process").exec;

const WEBPACK_WATCH = ["src/**/*.js", "src/**/*.scss"];
const WEBPACK_OUT = webpackConfig.output.path;
const ELEVENTY_OUT = "_site";
const FILES_TO_DELETE = [WEBPACK_OUT, "_layout/webpack.head.html", "_site"];
const ELEVENTY_WATCH = ["**/*", "!src", "!_site", WEBPACK_OUT];

function clean(cb) {
  del(FILES_TO_DELETE, cb);
}

function webpackBuild(cb) {
  webpack(webpackConfig, function(err, stats) {
    console.log(
      stats.toString({
        colors: true
      })
    );
    cb(err || stats.hasErrors());
  });
}

function eleventyBuild(cb) {
  exec("eleventy", function(err, stdout, stderr) {
    console.log(stdout);

    if (!err) {
      src(["js", "css"].map(ext => `${WEBPACK_OUT}/*.${ext}`)).pipe(
        dest(ELEVENTY_OUT)
      );
    }

    cb(err);
  });
}

function watcher() {
  browserSync.init({
    server: {
      baseDir: ELEVENTY_OUT
    }
  });

  function updating(cb) {
    browserSync.notify("Compiling, please wait!");
    cb();
  }

  function update(cb) {
    browserSync.reload();
    cb();
  }

  watch(WEBPACK_WATCH, series(updating, webpackBuild));
  watch(ELEVENTY_WATCH, series(eleventyBuild, update));
}

/*
 * watch flow
 *
 * - watch webpack related files to trigger webpack rebuild
 * - watch eleventy content to trigger eleventy rebuid
 */
exports.watch = series(clean, webpackBuild, eleventyBuild, watcher);
exports.clean = clean;

/*
 * build flow
 *
 * 1. build webpack js + css
 * 2. build eleventy
 * 3. copy webpack js/css in the _site
 */
exports.build = series(clean, webpackBuild, eleventyBuild);

Neat! Cool use of Gulp!

watch(WEBPACK_WATCH, webpackBuild);

Could it work with Webpack's HMR?

WEBPACK_WATCH

I guess it's duplicated from webpack.config.js?