How Does Server-Side Rendering Influence First Input Delay (FID), and What Are the Best Practices to Enhance It?


Server-side rendering (SSR) influences First Input Delay (FID) by providing a faster initial load and better interactivity, reducing the time to First Contentful Paint (FCP). However, optimizing SSR involves specific best practices such as reducing JavaScript payloads, implementing progressive hydration, and using web workers. Here’s a detailed guide on how to leverage SSR to enhance FID.

Understanding First Input Delay (FID)

First Input Delay (FID) measures the time from when a user first interacts with a page (e.g., by clicking a link, tapping a button) to the time when the browser begins to process that interaction. FID is crucial as it directly impacts user experience and page responsiveness.

Impact of Server-Side Rendering on FID

Improved Initial Render

SSR improves the initial render by sending a fully rendered HTML page to the browser. This can significantly speed up the First Contentful Paint (FCP), which indirectly contributes to a better FID because the sooner a page is visually ready, the sooner it can respond to user interactions.

Reduced JavaScript Execution

With SSR, the initial HTML does not rely heavily on client-side JavaScript to render the page. This reduces the JavaScript execution time on the client, leading to quicker browser readiness for user inputs, thereby enhancing FID.

Best Practices to Enhance FID with SSR

Optimize JavaScript Payloads

Minimize and split JavaScript bundles to ensure they are loaded and executed as quickly as possible. Use techniques like code-splitting and tree-shaking to include only the necessary JavaScript for the initial render. [Optimize JavaScript, 2023]

Progressive Hydration

Implement progressive hydration, which means gradually adding interactivity to the server-rendered HTML. This approach allows the initial HTML to be interactive sooner, as JavaScript is loaded and executed in smaller, manageable chunks. [Progressive Hydration, 2022]

Use Web Workers

Utilize web workers to offload heavy JavaScript computations from the main thread. This helps in keeping the main thread free to respond to user interactions, thereby reducing FID. [Using Web Workers, 2023]

Prioritize Critical Resources

Ensure that critical resources such as CSS and essential JavaScript for initial interactivity are loaded first. Use <link rel="preload"> and <link rel="prefetch"> to load these resources efficiently. [Preload Critical Assets, 2022]

Additional Techniques

Server-Side Caching

Implement server-side caching to deliver pre-rendered pages quickly. This reduces the time the server takes to respond to requests, allowing the browser to start processing the page sooner. [What is Caching?, 2023]

Reduce TTFB (Time to First Byte)

Optimize your server infrastructure to reduce the Time to First Byte. Using a Content Delivery Network (CDN) can help by serving content from servers closer to the user. [Time to First Byte (TTFB), 2020]


Enhancing FID through server-side rendering involves a combination of optimized JavaScript, progressive hydration, efficient use of web workers, and prioritizing critical resources. By following these best practices, you can significantly improve the responsiveness and user interaction experience of your web pages.