The IntersectionObserver interface's read-only root property identifies the Element or Document whose bounds are treated as the bounding box of the viewport for the element which is the observer's target. If the root is null, then the bounds of the actual document viewport are used.


var root = intersectionObserver.root;


A Element or Document object whose bounding box is used as the bounds of the viewport for the purposes of determining how much of the target element is visible. The intersection of this bounding rectangle, offset by any margins specified in the options passed to the IntersectionObserver() constructor, the target element's bounds, minus the bounds of every element or other object which overlaps the target element, is considered to be the visible area of the target element.

If root is null, then the owning document is used as the root, and the bounds its viewport (that is, the visible area of the document) are used as the root bounds.


This example sets the border of the intersection observer's root element to be a 2-pixel medium green line. = "2px solid #44aa44";


Specification Status Comment
Intersection Observer
The definition of 'IntersectionObserver' in that specification.
Working Draft Initial definition

Browser compatibility

Update compatibility data on GitHub
ChromeEdgeFirefoxInternet ExplorerOperaSafariAndroid webviewChrome for AndroidFirefox for AndroidOpera for AndroidSafari on iOSSamsung Internet
Chrome Full support 51Edge Full support 15Firefox Full support 55
Full support 55
No support 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.
IE No support NoOpera Full support YesSafari Full support 12.1WebView Android Full support 51Chrome Android Full support 51Firefox Android ? Opera Android ? Safari iOS Full support 12.2Samsung Internet Android Full support 5.0


Full support  
Full support
No support  
No support
Compatibility unknown  
Compatibility unknown
Experimental. Expect behavior to change in the future.
Experimental. Expect behavior to change in the future.
User must explicitly enable this feature.
User must explicitly enable this feature.

See also