What is Code Splitting?
A technique that breaks your JavaScript bundle into smaller chunks that are loaded on demand, reducing initial page load time by only sending the code needed for the current page.
In plain English
Code splitting is like a textbook with detachable chapters. Instead of carrying the entire 1,000-page book to class every day, you bring only the chapter you need. The rest stays available — you just grab it when you need it.
How it works
Instead of shipping one large JavaScript bundle, code splitting divides it into chunks based on routes, components, or features. When a user visits a page, only the code for that page is loaded. Additional code is fetched asynchronously when the user navigates to other pages. Next.js does route-based code splitting automatically. Dynamic imports (React.lazy) enable component-level splitting.
Why it matters for AI-built apps
AI-generated apps often import everything at the top level, creating enormous JavaScript bundles that slow down initial page loads. A single 2MB bundle forces users to download and parse code for features they may never use. Code splitting can reduce initial load times by 50–70%, dramatically improving user experience and Core Web Vitals.
Common issues
Not using dynamic imports for large dependencies, importing entire libraries when only a small part is needed (import everything from lodash vs lodash/get), not lazy-loading below-the-fold components, too many small chunks causing excessive HTTP requests, and not preloading chunks for likely next navigations.
Best practices
Next.js handles route-level splitting automatically — each page is a separate chunk. Use dynamic imports (next/dynamic) for heavy components that aren't immediately visible. Analyze your bundle with @next/bundle-analyzer to find the biggest chunks. Lazy-load heavy libraries (chart libraries, editors, maps). Preload chunks for likely navigation paths.
Frequently asked questions
Does Next.js handle code splitting automatically?
Yes, Next.js automatically splits code at the route level — each page only loads the JavaScript it needs. However, you still need to handle component-level splitting manually using next/dynamic for large components, and be mindful of import patterns that pull in large libraries. Use @next/bundle-analyzer to see what's in each chunk.
How do I know if my bundle is too large?
Run 'npx @next/bundle-analyzer' to visualize your bundles. As a rule of thumb, if your initial JavaScript exceeds 200KB gzipped, you likely need more splitting. Check Core Web Vitals — a low Total Blocking Time (TBT) and fast Largest Contentful Paint (LCP) indicate good splitting. Google Lighthouse also flags excessive JavaScript.
Check your app
Get a professional review of your app at a fixed price.
Security Scan
Black-box review of your public-facing app. No code access needed.
- OWASP Top 10 checks
- SSL/TLS analysis
- Security headers
- Expert review within 24h
Code Audit
In-depth review of your source code for security, quality, and best practices.
- Security vulnerabilities
- Code quality review
- Dependency audit
- AI pattern analysis
Complete Bundle
Both scans in one package with cross-referenced findings.
- Everything in both products
- Cross-referenced findings
- Unified action plan
100% credited toward any paid service. Start with an audit, then let us fix what we find.
Worried about code splitting in your app?
Get a professional code audit ($19) or book a free call to discuss your concerns.