Web/API/LayoutShift

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.

Properties

LayoutShift.value: Returns the impact fraction (fraction of the viewport that was shifted) times the distance fraction (distance moved as a fraction of viewport).
LayoutShift.hadRecentInput: Returns true if there was a user input in the past 500 milliseconds.
LayoutShift.lastInputTime: Returns the time of the most recent user input.
LayoutShift.sources: Returns an array of LayoutShiftAttribution objects with information on the elements that were shifted.

Methods

LayoutShift.toJSON(): 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	Status	Comment
Layout Instability APIThe definition of 'LayoutShift' in that specification.	Editor's Draft	Initial definition.

Browser compatibility

Update compatibility data on GitHub

	Desktop						Mobile
	Chrome	Edge	Firefox	Internet Explorer	Opera	Safari	Android webview	Chrome for Android	Firefox for Android	Opera for Android	Safari on iOS	Samsung Internet
`LayoutShift` Experimental'	Chrome Full support 77	Edge Full support 80	Firefox No support No	IE No support No	Opera Full support Yes	Safari No support No	WebView Android Full support 77	Chrome Android Full support 77	Firefox Android No support No	Opera Android Full support Yes	Safari iOS No support No	Samsung Internet Android Full support 12.0
`hadRecentInput` Experimental'	Chrome Full support 77	Edge Full support 80	Firefox No support No	IE No support No	Opera Full support Yes	Safari No support No	WebView Android Full support 77	Chrome Android Full support 77	Firefox Android No support No	Opera Android Full support Yes	Safari iOS No support No	Samsung Internet Android Full support 12.0
`lastInputTime` Experimental'	Chrome Full support 77	Edge Full support 80	Firefox No support No	IE No support No	Opera Full support Yes	Safari No support No	WebView Android Full support 77	Chrome Android Full support 77	Firefox Android No support No	Opera Android Full support Yes	Safari iOS No support No	Samsung Internet Android Full support 12.0
`toJSON` Experimental'	Chrome Full support 77	Edge Full support 80	Firefox No support No	IE No support No	Opera Full support Yes	Safari No support No	WebView Android Full support 77	Chrome Android Full support 77	Firefox Android No support No	Opera Android Full support Yes	Safari iOS No support No	Samsung Internet Android Full support 12.0
`value` Experimental'	Chrome Full support 77	Edge Full support 80	Firefox No support No	IE No support No	Opera Full support Yes	Safari No support No	WebView Android Full support 77	Chrome Android Full support 77	Firefox Android No support No	Opera Android Full support Yes	Safari iOS No support No	Samsung Internet Android Full support 12.0

Legend

Full support: Full support
No support: No support
Experimental. Expect behavior to change in the future.': Experimental. Expect behavior to change in the future.

LayoutShift by Mozilla Contributors is licensed under CC-BY-SA 2.5.