LayoutShift
Experimental: This is an experimental technology
Check the Browser compatibility table carefully before using this in production.
The LayoutShift
interface of the Layout Instability API provides insights into the stability of web pages based on movements of the elements on the page.
Instance properties
LayoutShift.value
Experimental-
Returns the
impact fraction
(fraction of the viewport that was shifted) times thedistance fraction
(distance moved as a fraction of viewport). LayoutShift.hadRecentInput
Experimental-
Returns
true
if there was a user input in the past 500 milliseconds. LayoutShift.lastInputTime
Experimental-
Returns the time of the most recent user input.
LayoutShift.sources
Experimental-
Returns an array of
LayoutShiftAttribution
objects with information on the elements that were shifted.
Instance methods
LayoutShift.toJSON()
Experimental-
Converts the properties to JSON.
Examples
The following example shows how to capture layout shifts and log them to the console.
Note that in this example data is only sent to the server when the user leaves the tab.
// Catch errors since some browsers throw when using the new `type` option.
// https://bugs.webkit.org/show_bug.cgi?id=209216
try {
let cumulativeLayoutShiftScore = 0;
const observer = new PerformanceObserver((list) => {
for (const entry of list.getEntries()) {
// Only count layout shifts without recent user input.
if (!entry.hadRecentInput) {
cumulativeLayoutShiftScore += entry.value;
}
}
});
observer.observe({type: 'layout-shift', buffered: true});
document.addEventListener('visibilitychange', () => {
if (document.visibilityState === 'hidden') {
// Force any pending records to be dispatched.
observer.takeRecords();
observer.disconnect();
console.log('CLS:', cumulativeLayoutShiftScore);
}
});
} catch (e) {
// Do nothing if the browser doesn't support this API.
}
Specifications
Specification |
---|
Layout Instability # sec-layout-shift |
Browser compatibility
BCD tables only load in the browser