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

The IntersectionObserver interface's read-only rootMargin property is a string with syntax similar to that of the CSS margin property. Each side of the rectangle represented by rootMargin is added to the corresponding side in the root element's bounding box before the intersection test is performed. This lets you, for example, adjust the bounds outward so that the target element is considered 100% visible even if a certain number of pixels worth of width or height is clipped away, or treat the target as partially hidden if an edge is too close to the edge of the root's bounding box.

See The root element and root margin in Intersection Observer API for a more in-depth look at the root margin and how it works with the root's bounding box.


var marginString = IntersectionObserver.rootMargin;


A string, formatted similarly to the CSS margin property's value, which contains offsets for one or more sides of the root's bounding box. These offsets are added to the corresponding values in the root's bounding box before the intersection between the resulting rectangle and the target element's bounds.

The string returned by this property may not match the one specified when the IntersectionObserver was instantiated. The browser is permitted to alter the values

If rootMargin isn't specified when the object was instantiated, it defaults to the string "0px 0px 0px 0px", meaning that the intersection will be computed between the root element's unmodified bounds rectangle and the target's bounds.  The root element and root margin in Intersection Observer API describes how the rootMargin is used in more detail.


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

Browser compatibility

FeatureChromeEdgeFirefoxInternet ExplorerOperaSafari
Basic support5115


53 — 551

No ? ?
FeatureAndroid webviewChrome for AndroidEdge mobileFirefox for AndroidOpera AndroidiOS SafariSamsung Internet
Basic support5151 Yes ? ? ?5.0

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: fscholz, UsainBloot, Sheppy
Last updated by: fscholz,