gulpfile.js

const { src, dest, watch, series } = require('gulp');
const sass = require('gulp-sass');
const postcss = require('gulp-postcss');
const cssnano = require('cssnano');
const terser = require('gulp-terser');
const browsersync = require('browser-sync').create();

// Sass Task
function scssTask(){
  return src('src/assets/sass/style.scss', { sourcemaps: true })
    .pipe(sass())
    .pipe(postcss([cssnano()]))
    .pipe(dest('src/assets/css', { sourcemaps: '.' }));
}

// Browsersync Tasks
function browsersyncServe(cb){
  browsersync.init({
    server: {
      baseDir: './'
    }
  });
  cb();
}

function browsersyncReload(cb){
  browsersync.reload();
  cb();
}

// Watch Task
function watchTask(){
  watch('**/*', browsersyncReload);
  watch(['src/assets/sass/**/*.scss'], series(scssTask, browsersyncReload));
}

// Default Gulp task
exports.default = series(
  scssTask,
  browsersyncServe,
  watchTask
);