This is an experimental technology
Because this technology's specification has not stabilized, check the compatibility table for usage in various browsers. Also note that the syntax and behavior of an experimental technology is subject to change in future versions of browsers as the specification changes.

The IntersectionObserverEntry interface's read-only intersectionRatio property tells you how much of the target element is currently visible within the root's intersection ratio, as a value between 0.0 and 1.0.


var intersectionRatio = IntersectionObserverEntry.intersectionRatio;


A number between 0.0 and 1.0 which indicates how much of the target element is actually visible within the root's intersection rectangle. More precisely, this value is the ratio of the area of the intersection rectangle (intersectionRect) to the area of the target's bounds rectangle (boundingClientRect).

If the area of the target's bounds rectangle is zero, the returned value is 1 if isIntersecting is true or 0 if not.


In this simple example, an intersection callback sets each target element's opacity to the intersection ratio of that element with the root.

function intersectionCallback(entries) {
  entries.forEach(function(entry) { = entry.intersectionRatio;

To see a more concrete example, take a look at "Handling intersection changes" in Timing element visibility with the Intersection Observer API.


Specification Status Comment
Intersection Observer
The definition of 'IntersectionObserverEntry.intersectionratio' in that specification.
Editor's Draft Initial definition

Browser compatibility

FeatureChromeEdgeFirefoxInternet ExplorerOperaSafari
Basic Support5115

53 — 551


No ? ?
FeatureAndroidChrome for AndroidEdge mobileFirefox for AndroidIE mobileOpera AndroidiOS Safari
Basic Support5151 (Yes) ? No ? ?

1. From version 53 until version 55 (exclusive): this feature is behind the dom.IntersectionObserver.enabled preference (needs to be set to true). To change preferences in Firefox, visit about:config.

Document Tags and Contributors

 Contributors to this page: tschwartz, fscholz, Sheppy
 Last updated by: tschwartz,