ExpressJs + Gulp + Browser Sync + SASS + JS

app.js

'use strict';

// simple express server
const express = require('express');
const app = express();
const router = express.Router();
const path = require('path');
app.use(express.static('public'));
app.get('/', function(req, res) {
    res.sendFile(path.join(__dirname+'/pages/index.html'))
});

app.listen(5000);

gulpfile.js

const gulp = require('gulp');
const browserSync = require('browser-sync');
const nodemon = require('gulp-nodemon');
const sass = require('gulp-sass');
const autoprefixer = require('autoprefixer');
const cssnano = require('cssnano');
const sourcemaps = require('gulp-sourcemaps');
const postcss = require('gulp-postcss');

const cleanCSS = require('gulp-clean-css');
const uglify = require('gulp-uglify');

// sass.compiler = require('sass')
gulp.task('sass', () => {
  return gulp
    .src('scss/main.scss')
    .pipe(sourcemaps.init())
    .pipe(sass())
    .pipe(postcss([autoprefixer(), cssnano()]))
    .pipe(cleanCSS())
    .pipe(sass({ errLogToConsole: true }))
    .pipe(sourcemaps.write('.'))
    .pipe(gulp.dest('./public/css'));
});
gulp.task('copy', () => {
  gulp.src('./node_modules/simple-line-icons/fonts/*').pipe(gulp.dest('./public/fonts'));
  gulp.src('./node_modules/font-awesome/fonts/*').pipe(gulp.dest('./public/fonts'));
});

gulp.task('sass:watch', () => {
  return gulp.watch('./scss/**/*.scss', ['sass']);
});

gulp.task('js', () => {
  return gulp
    .src('js/main.js')
    .pipe(uglify())
    .pipe(gulp.dest('./public/js'));
});
gulp.task('nodemon', cb => {
  let started = false;
  return nodemon({
    script: 'app.js',
  }).on('start', () => {
    if (!started) {
      cb();
      started = true;
    }
  });
});

gulp.task(
  'browser-sync',
  gulp.series('nodemon', () => {
    browserSync.init(null, {
      proxy: 'http://localhost:5000',
      files: ['public/**/*.*', 'pages/**/*.*'],
      port: 9001,
    });
  })
);

gulp.task('serve', gulp.series('browser-sync', () => {}));
gulp.task('watch', gulp.parallel('serve', 'sass', 'js', 'copy'));

gulp.watch(['scss/**/*.scss'], gulp.series('sass'));
gulp.watch(['js/**/*.js'], gulp.series('js'));

package.json

{
  "name": "watch",
  "version": "1.0.0",
  "description": "Watch theme",
  "main": "app.js",
  "scripts": {
    "test": "echo \"Error: no test specified\" && exit 1"
  },
  "author": {
    "name": "Webvi Viet Nam",
    "email": "lienhe@webvi.vn",
    "url": "http://webvi.vn"
  },
  "license": "PRIVATE",
  "dependencies": {
    "express": "^4.17.1"
  },
  "devDependencies": {
    "autoprefixer": "^9.6.1",
    "browser-sync": "^2.26.7",
    "cssnano": "^4.1.10",
    "gulp": "^4.0.2",
    "gulp-clean-css": "^4.2.0",
    "gulp-concat": "^2.6.1",
    "gulp-nodemon": "^2.4.2",
    "gulp-postcss": "^8.0.0",
    "gulp-sass": "^4.0.2",
    "gulp-sourcemaps": "^2.6.5",
    "gulp-uglify": "^3.0.2"
  }
}