What is codesplitting?
Codesplitting is a technique used in web development to break a large bundle of JavaScript code into smaller, separate pieces (or “chunks”). Instead of loading the entire codebase at once, the browser only loads the pieces it needs for the current page or feature, and fetches other pieces later when they’re required.
Let's break it down
- Imagine a book where every chapter is printed in one huge volume. You have to carry the whole book even if you only need one chapter.
- With codesplitting, that book is divided into individual chapters that can be taken out one at a time.
- In practice, a build tool (like Webpack, Rollup, or Vite) creates separate files for each chunk.
- When the app runs, it loads the main chunk first, then dynamically loads other chunks when the user navigates to a new route or triggers a feature.
Why does it matter?
- Faster initial load: Users download less code up front, so the page appears quicker.
- Better performance on slow connections or low‑end devices because they only process what they need.
- Reduced memory usage: The browser holds fewer unused scripts in memory.
- Improves perceived responsiveness, leading to happier users and better SEO rankings.
Where is it used?
- Single‑page applications (SPAs) built with React, Vue, Angular, or Svelte often use codesplitting for route‑based loading.
- Large e‑commerce sites that have many product pages, each with its own heavy components.
- Dashboard or admin panels where different sections (charts, tables, settings) are loaded only when accessed.
- Any web app that wants to optimize load time and resource usage, especially progressive web apps (PWAs).
Good things about it
- Speed: Smaller initial bundles mean quicker page render.
- Scalability: As the app grows, you can keep adding chunks without hurting the first load.
- User experience: Users see content faster and experience fewer “jank” moments.
- Network efficiency: Only the code that’s actually needed travels over the network.
- Cache friendliness: Unchanged chunks can stay cached while new ones are added.
Not-so-good things
- Complexity: Setting up and configuring codesplitting adds extra steps to the build process.
- Potential latency: Loading a new chunk on demand can cause a brief delay if the network is slow.
- Debugging challenges: Errors may appear in dynamically loaded chunks, making stack traces harder to read.
- Over‑splitting: Creating too many tiny chunks can increase the number of HTTP requests, negating performance gains.
- Tooling limitations: Some older libraries or frameworks may not support dynamic imports cleanly.