Performance has always been one of the biggest concerns in modern web development, especially now that users expect websites to load instantly. Drupal 10, with its modern frontend tools and support for advanced asset management, gives developers powerful ways to optimize load times. One of the most effective techniques is code splitting. If you’re new to the idea, code splitting may sound like something complicated or deeply technical, but it’s actually a simple concept: load only the code people need, when they need it. In this article, we’ll explore what code splitting looks like in Drupal 10, why it matters, the tools it uses, and how you can start applying it to improve your site’s performance.
What Is Code Splitting?
Code splitting is a performance optimization technique where JavaScript and CSS assets are divided into smaller chunks. Instead of bundling everything into one large file, the browser loads only the relevant pieces based on the page the visitor is viewing.
This helps:
- Reduce initial load time
- Improve perceived performance
- Cut down on unused code
- Make interactions feel smoother
Frameworks such as React and Vue have used this technique for years, but Drupal 10’s modern frontend foundation makes it easier to apply the same practice.
Attribution: The core idea of code splitting is widely credited to modern JavaScript bundlers like Webpack, Rollup, and Vite.
How Drupal 10 Supports Code Splitting
With the introduction of Drupal 10, the platform encourages a modern workflow that integrates well with JavaScript bundlers. Developers can use tools like Webpack, Vite, and ESBuild to break assets into smaller pieces and tell Drupal which pages should load which assets.
Here are some of the ways Drupal 10 supports code splitting.
1. Library Definitions
Drupal uses library YAML files to attach front-end assets in a controlled way. This is the foundation of code splitting because you can register multiple libraries and attach them only when required.
Example use cases:
- Load a slider script only on a page with sliders
- Attach form validation only to pages with forms
- Add admin JS only inside the admin theme
This prevents your site from loading unnecessary assets everywhere.
2. Conditional Asset Loading
Drupal 10 lets developers attach libraries conditionally through:
- hook_page_attachments
- hook_node_view
- Controller-based attachments
- Twig template attachments
This gives you full control. Instead of loading a single giant JavaScript bundle for every visitor, you load targeted libraries depending on the route, entity type, or view mode.
3. Support for Modern Build Tools
Drupal doesn’t restrict developers to outdated workflows. It works well with bundlers like Webpack or Vite, which handle the heavy lifting of splitting assets into chunks.
These bundles might contain:
- A main JS file
- Several dynamic import chunks
- Page-specific components
Drupal only needs you to register the output files through a library definition.
Why Code Splitting Matters for Drupal Websites
Most Drupal sites are heavy by nature. They often include:
- Multiple modules
- Complex pages
- Many third-party libraries
- Rich interactive components
Without code splitting, your site may load scripts that the visitor will never use. For example:
- A checkout JavaScript file loading on the homepage
- A photo gallery script loading on blog posts
- Admin toolbar assets loading on the public theme
Every unnecessary file adds weight and slows the user experience. Code splitting changes that.
Real Benefits You’ll Notice
Faster First Load
Visitors no longer wait for one giant JS bundle. They get the essential UI faster.
Better Mobile Experience
Mobile users benefit the most since their bandwidth is often slower.
Improved Core Web Vitals
Google measures loading speed and interactivity for SEO. Code splitting directly improves metrics like:
- LCP (Largest Contentful Paint)
- FID (First Input Delay)
- TTI (Time to Interactive)
Lower Resource Usage
Less JavaScript means fewer CPU cycles spent parsing and executing code. This is especially important on mid-range phones.
Where Code Splitting Helps the Most in Drupal 10
Here are common areas where it brings clear improvements:
1. Custom Themes
Modern themes often use:
- Carousels
- Modals
- Animations
- Reactive components
Instead of loading everything globally, split them into component-level libraries.
2. Single Page Applications (SPA) or Decoupled Apps
Dynamic imports are very common here. Drupal can serve as the backend while JS chunks load individually in the frontend.
3. Heavy Admin Pages
Admin themes like Claro and Gin can benefit from separating form-specific JavaScript from listing pages.
4. Commerce Pages
Checkout flows shouldn’t load on product listing pages. Code splitting fixes this.
Tips for Implementing Code Splitting in Drupal 10
Here are practical ideas developers can start using:
- Split your theme’s JavaScript into component-level files.
- Use build tools like Webpack or Vite to generate optimized bundles.
- Define separate libraries in YAML instead of one large file.
- Attach libraries conditionally in Twig templates.
- Use lazy loading for large interactive components.
- Audit your site to see which scripts load globally and move them to local loading instead.
Final Thoughts
Code splitting is one of the best ways to improve performance in Drupal 10, especially now that the platform embraces modern frontend workflows. It helps you load only the resources that matter, leading to a faster, cleaner, and more efficient experience for both users and administrators.
By learning how to define smaller libraries, conditionally attach assets, and integrate modern bundling tools, you’ll be able to deliver Drupal sites that feel as fast and polished as any modern web application.
If you’re looking to improve your Drupal 10 performance, code splitting is truly a technique worth mastering.