How to optimize website performance to improve FID (First Input Delay) in Core Web Vitals?

When optimizing website performance to improve FID (First Input Delay) in Core Web Vitals, the core is to reduce main thread blocking time and ensure that user interactions can be quickly responded to by the browser. FID measures the delay from the user's first interaction (such as clicking a button) to the browser starting to process it, which is mainly affected by the busyness of the main thread. Optimization directions include: - JavaScript execution optimization: Remove unused code (e.g., Tree Shaking), lazy load non-critical JS (using async/defer attributes), and split long tasks (break down complex operations into short tasks). - Third-party script management: Asynchronously load third-party scripts such as ads and analytics tools to prevent them from seizing the main thread; preconnect to critical domain names to reduce connection establishment time. - Resource priority adjustment: Inline critical CSS to reduce rendering blocking, compress JS/CSS files (e.g., using Gzip/Brotli), and reduce the occupation of main thread by resource loading. You can use Lighthouse or the Performance panel in Chrome DevTools to locate the source of main thread blocking, prioritize optimizing scripts that affect the user's first interaction, and gradually control FID within 200 milliseconds (the good standard for Core Web Vitals).