What Are the Most Common Pitfalls That Increase First Input Delay (FID) and How Can They Be Avoided During Website Development?

Summary

First Input Delay (FID) measures the time from when a user first interacts with a page (e.g., by clicking a link) to the time when the browser is able to begin processing event handlers in response to that interaction. Common pitfalls that increase FID include heavy JavaScript execution, long-running tasks, and render-blocking resources. This guide provides strategies to mitigate these issues and improve FID.

Heavy JavaScript Execution

Minimize and Optimally Load JavaScript

Excessive JavaScript execution can significantly increase FID. By minimizing and deferring non-essential JavaScript, you can reduce the amount of work the main thread needs to do before it can respond to user interactions.

Example:

• Use code-splitting to break JavaScript into smaller, more manageable pieces [Reduce JavaScript Payloads with Code Splitting, 2023].
• Load non-critical JavaScript asynchronously or defer its loading until the first render has been completed [Defer Non-Critical JavaScript, 2023].

Long-Running Tasks

Break Up Long Tasks

Long tasks block the main thread and prevent it from being able to respond to user interactions in a timely manner. It's essential to identify and break up long-running tasks into smaller chunks.

Example:

• Use web workers to offload tasks to background threads [Using Web Workers, 2023].
• Identify long tasks using tools like the Chrome DevTools and break them up into smaller tasks [Identify Long Tasks, 2023].

Render-Blocking Resources

Optimize CSS and Font Loading

Render-blocking resources, such as CSS and web fonts, can delay the time it takes for the page to be interactive.

Strategies:

• Minimize CSS and use <link rel="preload"> to dynamically load critical CSS [Optimize CSS Delivery, 2022].
• Use the font-display: swap; property for web fonts to avoid invisible text during loading [Web Font Optimization, 2023].

Reduce Server Response Times

Improving server response times can influence FID by ensuring that the browser receives resources quickly and can start processing them sooner.

Suggestions:

• Utilize a Content Delivery Network (CDN) to reduce latency [Why Performance Matters, 2023].
• Implement server-side caching to speed up the delivery of responses [Time to First Byte (TTFB), 2020].

Reduce Main-Thread Work

Efficiently Process Third-Party Scripts

Third-party scripts can often introduce performance bottlenecks. It’s important to monitor and manage these scripts carefully.

Actions:

• Audit third-party scripts and remove any that are not essential [Third-Party JavaScript, 2023].
• Defer the loading of non-critical third-party scripts using the async or defer attributes [Efficiently Load Third-Party JavaScript, 2022].

Conclusion

Improving First Input Delay (FID) involves a combination of minimizing heavy JavaScript execution, breaking up long tasks, handling render-blocking resources efficiently, improving server response times, and managing third-party scripts. Applying these strategies will enhance the responsiveness of your website and offer a better user experience.

References

• [Reduce JavaScript Payloads with Code Splitting, 2023] Google. (2023).
• [Defer Non-Critical JavaScript, 2023] Google. (2023).
• [Using Web Workers, 2023] Mozilla. (2023).
• [Identify Long Tasks, 2023] Google. (2023).
• [Optimize CSS Delivery, 2022] Google. (2022).
• [Web Font Optimization, 2023] Google. (2023).
• [Why Performance Matters, 2023] Google. (2023).
• [Time to First Byte (TTFB), 2020] Google. (2020).
• [Third-Party JavaScript, 2023] Google. (2023).
• [Efficiently Load Third-Party JavaScript, 2022] Google. (2022).