![]() ![]() If the user tries to interact with the page when a task is in progress, here is what happens: A visual representation of FID. I once had a situation where a script that initialized a hidden form in a modal window caused very long tasks. There are many things that can cause this issue. In the example above are some JavaScript tasks that are blocking the main thread. The tasks marked in red are blocking the main thread and making the browser unresponsive to user input. Some of these tasks block the browser's main thread, making it unresponsive to the user’s input until a particular parsing/evaluating task is finished. The browser takes its time to load HTML code, fetch CSS and JavaScript files, parse them and evaluate scripts. But there’s a Lighthouse metric that closely correlates with FID and is actually used for improving the latter. Search Console (Core Web Vitals report)įield measurement is also a reason why you won’t find this metric listed in your local Lighthouse report, since Lighthouse is not an “in the field” tool.This means that Google actually tracks the user’s interaction, measures the parameter, and sends it to platforms such as: While most of the Lighthouse parameters can be measured “in the lab,” meaning that network/throttling/behavioral conditions can be emulated with software methods, First Input Delay is measured “in the field.” However, they have a different way of measuring FID, so Google strongly recommends looking at the 95th-99th percentiles for this particular metric. Core Web Vitals have a threshold of the 75th percentile of all page loads to meet this criterion for most of your users. To provide a good user experience, a page should have a First Input Delay of 100 milliseconds or less. However, scrolling and zooming are not considered a first interaction. This includes clicking a link, tapping a button, or custom JavaScript-driven events. What is First Input Delay?įirst Input Delay, or FID, measures the time it takes a page to start processing a user's first interaction with a page. Now, in the age of high competition among websites, Google has introduced Core Web Vitals, a set of several performance metrics that at this moment (2021) represents three aspects of the user experience: loading, interactivity, and loading stability. Of course, devs back then were thinking of website performance (me included), but without unified tools to measure it. In the past, when network connections were slow, websites were meant mostly for computers, and people were more willing to wait an extra second to access the info they needed. In this article, we’re going to take a look at another related parameter: First Input Delay. Previously in our Google Lighthouse series, we have already discussed website interactivity as represented by the Time To Interactive Lighthouse metric. ![]() First published on March 30, 2021, in Engineering Everything Insights Engineering News Product Culture Compliance First Input Delay (FID): website interactivity and responsiveness ![]()
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