gulpfile.js

var autoprefixer = require('gulp-autoprefixer');
var gulp = require('gulp');
var sass = require('gulp-sass');
var sourcemaps = require('gulp-sourcemaps');
var browserSync = require('browser-sync');
var useref = require('gulp-useref');
var uglify = require('gulp-uglify');
var gulpIf = require('gulp-if');
var cssnano = require('gulp-cssnano');
var imagemin = require('gulp-imagemin');
var cache = require('gulp-cache');
var del = require('del');
var runSequence = require('run-sequence');

// Basic Gulp task syntax
gulp.task('hello', function() {
  console.log('Hello Zell!');
})

// Development Tasks 
// -----------------

// Start browserSync server
gulp.task('browserSync', function() {
  browserSync({
    server: {
      baseDir: "app"
    },
    files: "**/*.html"
  })
})

gulp.task('sass', function() {
  return gulp.src('app/scss/styles.scss') // Gets only the styles.scss file
  .pipe(sourcemaps.init())  //Initializes the sourcemaps before the source files are piped through sass
  .pipe(sass().on('error', sass.logError)) // Passes it through a gulp-sass, log errors to console
    .pipe(autoprefixer({
      browsers: ['last 2 versions'],   //Automatically prefixes with vendors for the last two versions of every browser
      cascade: false
    }))
    .pipe(sourcemaps.write(/*'./'*/))   //Writing external sourcemaps
    .pipe(gulp.dest('app/css')) // Outputs it in the css folder
    .pipe(browserSync.reload({ // Reloading with Browser Sync
      stream: true
    }));
})

// Watchers
gulp.task('watch', function() {
  gulp.watch('app/scss/**/*.+(scss|sass)', ['sass']);
  gulp.watch('app/*.html', browserSync.reload);
  gulp.watch('app/js/**/*.js', browserSync.reload);
})

// Optimization Tasks 
// ------------------

// Optimizing CSS and JavaScript 
gulp.task('useref', function() {

  return gulp.src('app/*.html')
    .pipe(useref())
    .pipe(gulpIf('*.js', uglify()))
    .pipe(gulpIf('*.css', cssnano()))
    .pipe(gulp.dest('dist'));
});

// Optimizing Images 
gulp.task('images', function() {
  return gulp.src('app/images/**/*.+(png|jpg|jpeg|gif|svg)')
    // Caching images that ran through imagemin
    .pipe(cache(imagemin({
      interlaced: true,
    })))
    .pipe(gulp.dest('dist/images'))
});

// Copying fonts 
gulp.task('fonts', function() {
  return gulp.src('app/fonts/**/*')
    .pipe(gulp.dest('dist/fonts'))
})

// Cleaning 
gulp.task('clean', function(cb) {
   del.sync(['dist'], cb)
})

gulp.task('clean:dist', function() {
  return del.sync(['dist/**/*', '!dist/images', '!dist/images/**/*']);
});

// Build Sequences
// ---------------

gulp.task('default', function(callback) {
  runSequence(['sass', 'browserSync'], 'watch',
    callback
  )
})

gulp.task('build', function(callback) {
  runSequence(
    'clean:dist',
    'sass',
    ['useref', 'images', 'fonts'],
    callback
  )
})