Using file filters.

Creating Images, JS, and CSS(SASS) rule for ordering files

Installing Gulp and His Tasks

$ npm install gulp --save-dev
$ npm install gulp-sass --save-dev
$ npm install gulp-uglify --save-dev
$ npm install gulp-imagemin --save-dev

Determining Folder Structure

In this structure, we will use the app folder for development purposes, while the dist folder is used to contain optimized files for the production site.

|-app
    |-css/
    |-images/
    |-index.html
    |-js/
    |-scss/
|- dist/
|- gulpfile.js
|- node_modules/
|- package.json

Gulp Preprocessing

// Requires the gulp-sass plugin
var gulp = require('gulp'); 
    sass = require('gulp-sass');
    uglify = require('gulp-uglify');
    imagemin = require('gulp-imagemin');

Gulp Task

gulp.task('sass', function(){
  return gulp.src('app/scss/**/*.scss') //selection all files in this derectory
    .pipe(sass()) // Using gulp-sass
    .pipe(gulp.dest('dist'))
});
gulp.task('gulp-uglify', function(){
  return gulp.src('app/js/*.js')
    // Minifies only if it's a JavaScript file
    .pipe(uglify())
    .pipe(gulp.dest('dist'))
});
gulp.task('images', function(){
  return gulp.src('app/images/**/*.+(png|jpg|gif|svg)')
  .pipe(imagemin())
  .pipe(gulp.dest('dist/images'))
});

Gulp Watch

gulp.task('watch', function(){
  gulp.watch('app/js/**/*.js', ['gulp-uglify']); 
    gulp.watch('app/scss/**/*.scss', ['sass']);
    gulp.watch('app/images/**/*.*', ['images']);  
  // Other watchers
});
gulp.task('build', [`sass`, `gulp-uglify`, `images`], function (){
  console.log('Building files');
});
gulp.task('default', function() {});