Undescores (_s) build tooling

gulpfile.js

// Gulp.js configuration
'use strict';

const

  // Gulp and plugins
  gulp          = require('gulp'),
  gutil         = require('gulp-util'),
  newer         = require('gulp-newer'),
  imagemin      = require('gulp-imagemin'),
  sass          = require('gulp-sass'),
  postcss       = require('gulp-postcss'),
  deporder      = require('gulp-deporder'),
  concat        = require('gulp-concat'),
  stripdebug    = require('gulp-strip-debug'),
  uglify        = require('gulp-uglify')
;

// Browser-sync
var browsersync = false;

// PHP settings
const php = {
  src           : '**/*.php'
};

// image settings
const images = {
  src         : 'images/**/*',
  build       : 'images/'
};

// image processing
gulp.task('images', () => {
  return gulp.src(images.src)
    .pipe(newer(images.build))
    .pipe(imagemin())
    .pipe(gulp.dest(images.build));
});

// CSS settings
var css = {
  src         : 'sass/style.scss',
  watch       : 'sass/**/*',
  build       : '',
  sassOpts: {
    outputStyle     : 'nested',
    imagePath       : images.build,
    precision       : 3,
    errLogToConsole : true
  },
  processors: [
    require('postcss-assets')({
      loadPaths: ['images/'],
      basePath: '/',
      baseUrl: '/wp-content/themes/nordex-food/'
    }),
    require('autoprefixer')({
      browsers: ['last 2 versions', '> 2%']
    }),
    require('css-mqpacker'),
    require('cssnano')
  ]
};

// CSS processing
gulp.task('css', ['images'], () => {
  return gulp.src(css.src)
    .pipe(sass(css.sassOpts))
    .pipe(postcss(css.processors))
    .pipe(gulp.dest(css.build))
    .pipe(browsersync ? browsersync.reload({ stream: true }) : gutil.noop());
});

// JavaScript settings
const js = {
  src         : 'js/**/*',
  build       : 'js/',
  filename    : 'scripts.js'
};

// JavaScript processing
gulp.task('js', () => {

  return gulp.src(js.src)
    .pipe(deporder())
    .pipe(concat(js.filename))
    .pipe(stripdebug())
    .pipe(uglify())
    .pipe(gulp.dest(js.build))
    .pipe(browsersync ? browsersync.reload({ stream: true }) : gutil.noop());

});

// run all tasks
gulp.task('build', ['css', 'js']);

// Browsersync options
const syncOpts = {
  proxy       : 'localhost',
  files       : '**/*',
  open        : false,
  notify      : false,
  ghostMode   : false,
  ui: {
    port: 8001
  }
};


// browser-sync
gulp.task('browsersync', () => {
  if (browsersync === false) {
    browsersync = require('browser-sync').create();
    browsersync.init(syncOpts);
  }
});

// watch for file changes
gulp.task('watch', ['browsersync'], () => {

  // page changes
  gulp.watch(php.src, ['php'], browsersync ? browsersync.reload : {});

  // image changes
  gulp.watch(images.src, ['images']);

    // CSS changes
  gulp.watch(css.watch, ['css']);

  // JavaScript main changes
  gulp.watch(js.src, ['js']);

});

// default task
gulp.task('default', ['build', 'watch']);

package.json

{
  "name": "project-name",
  "version": "1.0.0",
  "scripts": {},
  "devDependencies": {
    "autoprefixer": "^7.1.3",
    "browser-sync": "^2.18.13",
    "css-mqpacker": "^6.0.1",
    "cssnano": "^3.10.0",
    "gulp": "^3.9.1",
    "gulp-concat": "^2.6.1",
    "gulp-deporder": "^1.1.0",
    "gulp-imagemin": "^3.3.0",
    "gulp-newer": "^1.3.0",
    "gulp-postcss": "^7.0.0",
    "gulp-sass": "^3.1.0",
    "gulp-strip-debug": "^1.1.0",
    "gulp-uglify": "^3.0.0",
    "gulp-util": "^3.0.8",
    "gulp-watch": "^4.3.11",
    "postcss-assets": "^4.2.0"
  }
}