This is an experimental technology
Check the Browser compatibility table carefully before using this in production.

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.target.style.opacity = entry.intersectionRatio;

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


Browser compatibilityUpdate compatibility data on GitHub

Chrome Edge Firefox Internet Explorer Opera Safari
Basic support 51 15 55
53 — 55
Disabled 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.
No ? ?
Android webview Chrome for Android Edge Mobile Firefox for Android Opera for Android iOS Safari Samsung Internet
Basic support 51 51 Yes ? ? ? 5.0

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