What Strategies Can I Employ to Reduce the Impact of Third-Party Scripts on First Input Delay (FID)?


Reducing the impact of third-party scripts on First Input Delay (FID) can be achieved by optimizing script handling, employing strategic loading techniques, and minimizing the usage of unnecessary third-party resources. This guide provides various strategies and examples to improve FID effectively.

Optimize Script Handling

Asynchronous and Deferred Loading

One effective strategy is to load third-party scripts asynchronously or defer their execution until after the main content has loaded. This ensures that the critical path is not blocked by script loading.

For example, adding the async or defer attribute in the script tag:

<script src="path/to/script.js" async></script>

This approach prevents the script from blocking the rendering process and can significantly reduce FID [Defer Non-Critical JavaScript, 2023].

Strategic Loading Techniques

Lazy Loading

Loading scripts only when they are needed can reduce their impact on FID. Lazy loading leverages techniques to load resources merely when they enter the viewport or become necessary for the user interaction.

For instance, you can use the IntersectionObserver API to determine when a resource comes into view:

  const observer = new IntersectionObserver((entries) => {
    entries.forEach(entry => {
      if (entry.isIntersecting) {
        const script = document.createElement('script');
        script.src = 'path/to/script.js';


This method ensures that scripts do not impact initial load and critical rendering times [Lazy Loading, 2023].

Critical Path Reduction

Prioritize loading essential scripts and deferring non-essential ones to minimize the critical rendering path. Inline small scripts necessary for initial load directly into the HTML.

For example:

// Critical JavaScript inline

Deferring non-essential scripts ensures faster rendering of initial content, enhancing FID [Understanding the Critical Rendering Path, 2023].

Minimize Third-Party Resource Usage

Auditing and Removing Unnecessary Scripts

Perform audits to identify and remove redundant or unused third-party scripts. Tools such as Lighthouse by Google can help audit and pinpoint scripts that negatively impact performance [Lighthouse, 2023].

Regular audits ensure your site does not carry unnecessary third-party burdens, thus improving FID.

Using Efficient Scripts

Select efficient and optimized third-party libraries and scripts. Smaller and well-optimized libraries can greatly reduce loading times and resource consumption.

For example, consider using lightweight libraries that are designed to be performance-friendly [Progressive Toolkit, 2023].

Monitoring and Continuous Optimization

Performance Monitoring Tools

Use monitoring tools like Google Web Vitals and PageSpeed Insights to measure and continuously monitor FID.

Regular monitoring helps identify new issues as they arise, enabling timely optimizations [Measure Performance, 2023].

Real-User Monitoring (RUM)

Implement Real-User Monitoring to gain insights into how actual users experience FID on your website, allowing for more data-driven and effective optimizations.

Tools like New Relic offer comprehensive monitoring solutions [New Relic, 2023].


By strategically optimizing the loading and handling of third-party scripts, regularly auditing and removing unnecessary scripts, and monitoring performance, you can significantly reduce the impact of third-party scripts on First Input Delay (FID). Adopting these practices will enhance user experience and improve overall site performance.