How to Implement Lazy Loading for JavaScript

Short answer

Lazy loading JavaScript means importing modules only when they are needed. This reduces the initial bundle size and speeds up page startup.

Steps

1. Use dynamic import() instead of static import for non-critical modules.
2. Combine dynamic imports with route-based splitting in frameworks like React or Vue.
3. Add loading indicators while the module fetches.
4. Preload critical chunks that are likely to be needed next.
5. Analyze the bundle with Webpack Bundle Analyzer to find candidates.

Tips

• Set a low priority for analytics and third-party scripts.
• Use React.lazy and Suspense for component-level splitting.
• Cache lazy-loaded chunks aggressively to avoid repeated downloads.

Common issues

• Network waterfalls can occur if too many modules load sequentially.
• Error boundaries are needed to catch failed dynamic imports.