First Input Delay (FID) measures the responsiveness of a website, quantifying the time from when a user first interacts with a site to when it actually responds. Improving FID involves optimizing how JavaScript is parsed and executed.
Common Issues Affecting FID:
- Heavy JavaScript execution
- Long tasks blocking the main thread
- Render-blocking scripts
- Large JavaScript bundles
- Third-party scripts
Solutions to Improve FID:
- Optimize JavaScript Execution:
- Break up long tasks into smaller, asynchronous tasks.
- Use web workers to run heavy computations off the main thread.
- Defer or asynchronously load non-critical JavaScript.
- Minimize Render-Blocking Scripts:
- Move critical JavaScript inline or load it asynchronously.
- Eliminate unnecessary JavaScript or reduce its impact.
- Reduce JavaScript Bundle Sizes:
- Use code splitting to load only the JavaScript needed for the current page.
- Tree-shake unused code from your bundles.
- Minify and compress JavaScript files.
- Optimize Third-Party Scripts:
- Review and remove any unnecessary third-party scripts.
- Load third-party scripts asynchronously or defer their loading.
- Use efficient APIs and only include essential functionalities from third-party libraries.
- Improve Browser Rendering Performance:
- Avoid large, complex layout changes that could block the main thread.
- Optimize CSS to reduce rendering times.
- Use modern web technologies like requestIdleCallback to perform non-urgent work during idle periods.
