The First Input Delay measurement is triggered even when the user clicks non-interactive elements like the page background. User Input Includes Clicks On Non-Interactive Elements If the user never interacts with the page, no first input entry will be recorded. Not every page view results in a FID entry. First Input Delay Measurements Don’t Always Occur While the measurement itself is straightforward, FID measurements have several quirks that you should be aware of. We can test the API’s behavior with a little code: NOTE: As a draft standard, there are occasionally changes to how FID is determined.
It is currently supported in Blink-based browsers, such as Chrome, Edge, and Opera.
The Event Timing API exposes first input delay measurements through JavaScript. Measuring First Input Delay With The Event Timing API JS frameworks like React and Angular are often culprits when coding mistakes cause excessive re-rendering.
#Input delay tester code#
Any poorly optimized code can cause this issue.
#Input delay tester free#
User inputs are blocked until the task finishes and the main thread is free to handle the input. Any long running task in JavaScript runs on the main thread. Long FID times occur even after all JavaScript has been loaded. Large bundles are often caused by excessive third party dependencies or the inclusion of code that is not needed by the current page. Inputs are delayed because they must wait for the page to load all referenced JavaScript. Large JavaScript bundles can take a long time for the browser to parse and evaluate. Both initial payload and ongoing execution can be culprits. Heavy JavaScript is the main cause of long first input delays. Slow JavaScript evaluation delays the user's first click (yellow).įirst Input Delay will be different for every application, but Google has provided basic guidance on acceptable FID times: First Input Delay threshold recommendations from Google. The page has some slow JavaScript which blocks the browser’s main thread on page load: First Input Delay Example. In this example, the FID is captured and shown in the console. It and other Core Web Vital metrics impact SEO because Google will soon consider them when ranking search results. FID measures this unresponsive time, but does not include the time taken in the event handlers themselves.įirst Input Delay isn’t just an important measure of user experience. The page appears unresponsive when the user interacts with a busy browser by either clicking or typing. First Input Delayĭelays to the first user input are caused when the browser is busy downloading assets, parsing scripts, or executing blocking operations. New measurements like First Input Delay are increasingly important as JavaScript and SPA’s do more work on the client side. It’s one of several Core Web Vital metrics that measure how real users perceive the performance of modern web applications. First Input Delay (FID) measures how long the browser took to respond to the first user input event.
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