The IntersectionObserver() constructor creates and returns a new IntersectionObserver object. The rootMargin, if specified, is checked to ensure it's syntactically correct, the thresholds are checked to ensure that they're all in the range 0.0 and 1.0 inclusive, and the threshold list is sorted in ascending numeric order. if the threshold list is empty, it's set to the array [0.0].


var observer = new IntersectionObserver(callback[, options]);


A function which is called when the percentage of the target element is visible crosses a threshold. The callback receives as input two parameters:
An array of IntersectionObserverEntry objects, each representing one threshold which was crossed, either becoming more or less visible than the percentage specified by that threshold.
The IntersectionObserver for which the callback is being invoked.
options Optional
An optional object which customizes the observer. If options isn't specified, the observer uses the document's viewport as the root, with no margin, and a 0% threshold (meaning that even a one-pixel change is enough to trigger a callback). You can provide any combination of the following options:
An Element or Document object which is an ancestor of the intended target, whose bounding rectangle will be considered the viewport. Any part of the target not visible in the visible area of the root is not considered visible.
A string which specifies a set of offsets to add to the root's bounding_box when calculating intersections, effectively shrinking or growing the root for calculation purposes. The syntax is approximately the same as that for the CSS margin property; see The root element and root margin in Intersection Observer API for more information on how the margin works and the syntax. The default is "0px 0px 0px 0px".
Either a single number or an array of numbers between 0.0 and 1.0, specifying a ratio of intersection area to total bounding box area for the observed target. A value of 0.0 means that even a single visible pixel counts as the target being visible. 1.0 means that the entire target element is visible. See Thresholds in Intersection Observer API for a more in-depth description of how thresholds are used. The default is a threshold of 0.0.

Return value

A new IntersectionObserver which can be used to watch for the visibility of a target element within the specified root crossing through any of the specified visibility thresholds. Call its observe() method to begin watching for the visibility changes on a given target.


The specified rootMargin is invalid.
One or more of the values in threshold is outside the range 0.0 to 1.0.


This example creates a new intersection observer which calls the function myObserverCallback every time the visible area of the element being observed changes by at least 10%.

let observer = new IntersectionObserver(myObserverCallback,
                   {threshold: 0.1});


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

Browser compatibility

ChromeEdgeFirefoxInternet ExplorerOperaSafariAndroid webviewChrome for AndroidFirefox for AndroidOpera for AndroidSafari on iOSSamsung Internet
IntersectionObserver() constructor
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 38Safari 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
root option can be a DocumentChrome Full support 81Edge Full support 81Firefox Full support 76IE No support NoOpera Full support 68Safari No support NoWebView Android Full support 81Chrome Android Full support 81Firefox Android No support NoOpera Android Full support 58Safari iOS No support NoSamsung Internet Android No support No


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.