gulpfile.js

var gulp = require('gulp');

var sass = require('gulp-sass');
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('testing', function () {
    console.log('Testing, testing, 1, 2, 3');
});*/

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

//Start browserSync server
gulp.task('browserSync', function () {
    browserSync({
        server: {
            baseDir: 'app'
        },
    })
});

gulp.task('sass', function () {
    return gulp.src('app/scss/**/*.scss')
        .pipe(sass()) //Converts Sass to CSS with gulp-sass
        .pipe(gulp.dest('app/css'))
        .pipe(browserSync.reload({
            stream: true
        }));
})

//Watchers
gulp.task('watch', ['browserSync', 'sass'], function () {
    gulp.watch('app/scss/**/*.scss', ['sass']);
    // Reloads the browser whenever HTML or JS files change
    gulp.watch('app/*.html', browserSync.reload);
    gulp.watch('app/js/**/*.js', browserSync.reload);
})

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

//Optimizing CSS and Javascript
//concatenates CSS and JS files into a single file
gulp.task('useref', function () {
    return gulp.src('app/*.html')
        .pipe(useref())
        // Minifies only if it's a JS file
        .pipe(gulpIf('*.js', uglify()))
        // Minifies only if it's a CSS file
        .pipe(gulpIf('*.css', cssnano()))
        .pipe(gulp.dest('dist'));
});

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

//Cleaning
//Cleaning up generated files automatically(ie deleting them)
/*gulp.task('clean:dist', function () {
    return del.sync('dist')
});*/

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

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

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