Question 1

How do I measure First Input Delay in my web app?

Accepted Answer

Inline the minified script from dist/first-input-delay.min.js in your document head and register a callback using perfMetrics.onFirstInputDelay() to capture the delay and event details for reporting or analysis.

Question 2

Is the First Input Delay library still supported?

Accepted Answer

No, it's archived and deprecated. Google has moved all development to the web-vitals library, which includes FID and other Core Web Vitals with active maintenance.

Question 3

Can I use First Input Delay with modern frameworks like React or Vue?

Accepted Answer

Yes, but you need to ensure the script is inlined in the head, which might require server-side rendering configuration or build tool adjustments to avoid conflicts.

Question 4

What's the difference between FID and Time to Interactive?

Accepted Answer

FID measures the actual delay after a user's first interaction, focusing on responsiveness, while Time to Interactive estimates when the page is fully ready for interaction, based on loading and execution.

Question 5

How do I report FID to Google Analytics?

Accepted Answer

Use the callback function to send an event to GA with the rounded delay value and event type, setting nonInteraction to true to exclude it from bounce rate calculations.

Question 6

Should I use first-input-delay or web-vitals for FID tracking?

Accepted Answer

Use web-vitals for new projects, as it includes FID and other metrics with ongoing updates. First-input-delay is only suitable for legacy systems where migration isn't feasible.

Question 7

What browsers does first-input-delay support?

Accepted Answer

It supports all major browsers, including Internet Explorer 9 and above, making it a reliable choice for older environments but less optimized for modern ES6+ features.

Polyfill - FID

What is Polyfill - FID?

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