Develop WordPress Themes Faster with Gulp

WordPress’ simple theme development is partly responsible for its success. A developer with front-end and PHP knowledge can consult the excellent Codex and get started on their next masterpiece.

Theme development is possible with just a text editor and graphics package, but modern toolsets can revolutionize your workflow. In this tutorial we’ll use Gulp to run tasks including:

copying newer PHP theme files
optimizing images
compiling Sass SCSS files into a single, minified CSS file
merging ordered JavaScript files, remove debugging statements and minifying
automatically refreshing the browser when files are updated.

What is Gulp?

Gulp is a JavaScript-based build system which takes your source files and transforms them into optimized versions. If you’re new to Gulp, please refer to An Introduction to Gulp.js for full installation and usage instructions. A summary of the initial steps:

Install Node.js.
Install Gulp globally: npm install gulp-cli -g
Create a project folder and navigate into it: mkdir mytheme followed by cd mytheme.
Initialize your project with npm: npm init

Your Project Files

A Gulp (or any) build process requires a set of original source files containing your unmodified code and images. These are processed, manipulated and minified to create build files.

WordPress is installed to a web server folder, perhaps /var/www/ on a Linux/Apache installation. Your WordPress theme must be defined in its own sub-folder within /wp-content/themes/. Therefore, the folder containing our built files could be /var/www/wp-content/themes/mytheme/. At a minimum, themes require two files:

a style.css stylesheet containing meta-data in comments at the top, and
an index.php template file.

Most themes contain many more files for presenting posts, pages, indexes, categories, tags, and errors. Cross-page partials such as headers and footers are usually defined as are image and JavaScript files.

You could place your source files somewhere within the mytheme folder. That may be useful if you’re distributing a theme to be downloaded, modified and built by others. However, for the purpose of this tutorial, we’re going to use a source folder which is inaccessible from the web server, e.g. ~/mytheme/. The benefits of this approach:

Your theme source files can be managed in a single folder and repository without polluting the build or WordPress folders.
The final built theme folder contains only the files it requires.
Gulp, its plug-ins and other applications are not contained in the theme folder. They cannot be accidentally copied to a production server which is unnecessary and could have security implications.

The source project folder requires a further four sub-folders:

template - the WordPress PHP theme files
images - images used by your theme
scss - Sass SCSS source files
js - any number of separate client-side JavaScript source files.

Install Dependencies

From the source folder (~/mytheme/), run the following npm command to install Gulp and all plug-ins as development dependencies:

npm install --save-dev autoprefixer browser-sync css-mqpacker cssnano gulp gulp-concat gulp-deporder➥gulp-imagemin gulp-newer gulp-postcss gulp-sass gulp-strip-debug gulp-uglify gulp-util ➥postcss-assets

A node_modules folder will be created which contains the module code. That should be omitted from your source control system (for Git users, add node_modules to your .gitignore file).

Create a Gulp Configuration File

Create a new gulpfile.js configuration file in the root of your source folder. Add this code to get started:

// Gulp.js configuration'use strict';
const
  // source and build folders  dir = {    src         : 'src/',    build       : '/var/www/wp-content/themes/mytheme/'  },
  // 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-syncvar browsersync = false;

// PHP settingsconst php = {  src           : dir.src + 'template/**/*.php',  build         : dir.build};
// copy PHP filesgulp.task('php', () => {  return gulp.src(php.src)    .pipe(newer(php.build))    .pipe(gulp.dest(php.build));});

We’re defining our default folders, loading modules, then creating a php task to copy new and updated files to the theme folder. The task has been kept intentionally simple to copy the PHP source files as-is.

Save gulpfile.js and create a few .php files in the source template folder. Then enter the following command:

gulp php

All the files will be copied to the theme folder (/var/www/wp-content/themes/mytheme/).

Image Processing

Image files can often be compressed further using tools such as imagemin. Add the following code to gulpfile.js:

// image settingsconst images = {  src         : dir.src + 'images/**/*',  build       : dir.build + 'images/'};
// image processinggulp.task('images', () => {  return gulp.src(images.src)    .pipe(newer(images.build))    .pipe(imagemin())    .pipe(gulp.dest(images.build));});

Save then run gulp images. Compressed versions of any new or updated images in the source images folder are copied to /var/www/wp-content/themes/mytheme/images/.

Sass Compilation

WordPress cannot use Sass files directly; you must compile to a single style.css file. Add the following code to gulpfile.js:

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

Launch this new task with gulp css to:

run the Gulp images task first (images may be required in your CSS)
compile the Sass code in the source scss/style.scss file using the fast LibSass compiler
use PostCSS to automatically add asset references, apply vendor prefixes, pack media queries together, and minify the resulting CSS code
output the stylesheet to /var/www/wp-content/themes/mytheme/style.css.
force a Browsersync CSS reload (more about that later).

The source scss/style.scss file must include the WordPress theme meta data at the top, e.g.

/*!    Theme Name: My Theme    Theme URI: http://www.sitepoint.com/    Description: Demonstration theme    Version: 1.0.0    Author: Craig Buckler (@craigbuckler)    Author URI: http://www.sitepoint.com/    Tags: Gulp
    License: MIT    License URI: http://opensource.org/licenses/mit-license.php*/
@import'_base';@import'_forms';@import'_tables';@import'components/_widget1';// etc...

It is important to use /*! as the first line. This ensures the cssnano minifier does not remove the comment and render your theme unusable.

The postcss-assets plugin allows you to refer to image assets using code such as:

.widget1 {  width: width('myimage.jpg');  height: height('myimage.jpg');  background-image: resolve('myimage.jpg');}

You can also inline images with automatic Base64 encoding:

.widget2 {  background-image: inline('myimage.jpg');}

JavaScript Processing

Add the following code to gulpfile.js:

// JavaScript settingsconst js = {  src         : dir.src + 'js/**/*',  build       : dir.build + 'js/',  filename    : 'scripts.js'};
// JavaScript processinggulp.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 this new task with gulp js to:

process all JavaScript files in the source js folder
order the files appropriately. Add comments at the top of your JavaScript files to declare dependencies, e.g. // requires: lib1.js or // requires: config.js lib1.js.
concatenate into a single file
strip all debugging and console logging statements
minify the code
output the resulting code to /var/www/wp-content/themes/mytheme/js/scripts.js.
force a Browsersync CSS reload (more about that later).

Run Everything

Rather than calling each task separately, we can add the following code to gulpfile.js:

// run all tasksgulp.task('build', ['php', 'css', 'js']);

You can now use gulp build to run the php, js, css and images tasks in parallel. (Note images is a dependency of the css task so we need not call it directly.)

Enable File Watching and Browsersync

Your workflow can be radically improved by:

Letting Gulp watch for file changes before launching the appropriate task.
Automatically reloading CSS and JavaScript files when they change (without a page refresh).
Automatically refreshing the page when a template file changes.

First, we need to define a browsersync task in gulpfile.js. This will create a proxy server to your web server running WordPress on localhost (change this domain or use an IP address as necessary):

// Browsersync optionsconst syncOpts = {  proxy       : 'localhost',  files       : dir.build + '**/*',  open        : false,  notify      : false,  ghostMode   : false,  ui: {    port: 8001  }};

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

Now add a watch task to run Browsersync, watch for file changes and run the appropriate task:

// watch for file changesgulp.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']);
});

Finally, add a default Gulp task which runs an initial build and starts the watch task:

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

Now run gulp from the command line. The console will display output which includes lines similar to:

[BS] Proxying: http://localhost[BS] Access URLs: -------------------------------------       Local: http://localhost:3000    External: http://192.168.1.99:3000 -------------------------------------          UI: http://localhost:8001 UI External: http://192.168.1.99:8001 -------------------------------------[BS] Watching files...

Rather than loading your development site from http://localhost/, enter the address http://localhost:3000/ or the External URL if you are viewing from another device. Your WordPress site will load as before but Gulp will watch for changes and apply the updates immediately. You’ll need never switch to your browser and click refresh again!

Hit Ctrl/Cmd + C when you want to stop Gulp processing.

Enhance Further

We’ve covered the basics of WordPress theme development with Gulp but there are several thousand plug-ins to aid your workflow. You could consider additional tasks to:

lint your PHP and JavaScript code
create WordPress theme styles from package.json infomation
cache-bust WordPress assets
automatically deploy your theme to a production server.

A few hours writing Gulp tasks could save many days of manual processing over the long term.