The ResizeObserverEntry interface represents the object passed to the ResizeObserver() constructor's callback function, which allows you to access the new dimensions of the Element or SVGElement being observed.

Properties

ResizeObserverEntry.borderBoxSize Read only
An object containing the new border box size of the observed element when the callback is run.
ResizeObserverEntry.contentBoxSize Read only
An object containing the new content box size of the observed element when the callback is run.
ResizeObserverEntry.contentRect Read only
A DOMRectReadOnly object containing the new size of the observed element when the callback is run. Note that this is better supported than the above two properties, but it is left over from an earlier implementation of the Resize Observer API, is still included in the spec for web compat reasons, and may be deprecated in future versions.
ResizeObserverEntry.target Read only
A reference to the Element or SVGElement being observed.

Note: The content box is the box in which content can be placed, meaning the border box minus the padding and border width. The border box encompasses the content, padding, and border. See The box model for further explanation.

Methods

None.

Examples

The following snippet is taken from the resize-observer-text.html (see source) example. This uses a simple feature detection test to see if the browser supports the newer contentBoxSize property — if so, it uses that to get the sizing data it needs. If not, it uses the older contentRect property.

const resizeObserver = new ResizeObserver(entries => {
  for (let entry of entries) {
    if(entry.contentBoxSize) {
      h1Elem.style.fontSize = Math.max(1.5, entry.contentBoxSize.inlineSize/200) + 'rem';
      pElem.style.fontSize = Math.max(1, entry.contentBoxSize.inlineSize/600) + 'rem';
    } else {
      h1Elem.style.fontSize = Math.max(1.5, entry.contentRect.width/200) + 'rem';
      pElem.style.fontSize = Math.max(1, entry.contentRect.width/600) + 'rem';
    }
  }
});

resizeObserver.observe(divElem);

Specifications

Specification Status Comment
Resize Observer
The definition of 'ResizeObserverEntry' in that specification.
Editor's Draft Initial definition.

Browser compatibility

Update compatibility data on GitHub
DesktopMobile
ChromeEdgeFirefoxInternet ExplorerOperaSafariAndroid webviewChrome for AndroidFirefox for AndroidOpera for AndroidSafari on iOSSamsung Internet
ResizeObserverEntryChrome Full support 64Edge No support NoFirefox Full support 69IE No support NoOpera Full support YesSafari No support NoWebView Android Full support 64Chrome Android Full support 64Firefox Android No support NoOpera Android Full support YesSafari iOS No support NoSamsung Internet Android Full support Yes
borderBoxSize
Experimental
Chrome No support NoEdge No support NoFirefox Full support 69IE No support NoOpera No support NoSafari No support NoWebView Android No support NoChrome Android No support NoFirefox Android No support NoOpera Android No support NoSafari iOS No support NoSamsung Internet Android No support No
contentBoxSize
Experimental
Chrome No support NoEdge No support NoFirefox Full support 69IE No support NoOpera No support NoSafari No support NoWebView Android No support NoChrome Android No support NoFirefox Android No support NoOpera Android No support NoSafari iOS No support NoSamsung Internet Android No support No
contentRectChrome Full support 64Edge No support NoFirefox Full support 69IE No support NoOpera Full support YesSafari No support NoWebView Android Full support 64Chrome Android Full support 64Firefox Android No support NoOpera Android Full support YesSafari iOS No support NoSamsung Internet Android Full support Yes
targetChrome Full support 64Edge No support NoFirefox Full support 69IE No support NoOpera Full support YesSafari No support NoWebView Android Full support 64Chrome Android Full support 64Firefox Android No support NoOpera Android Full support YesSafari iOS No support NoSamsung Internet Android Full support Yes

Legend

Full support  
Full support
No support  
No support
Experimental. Expect behavior to change in the future.
Experimental. Expect behavior to change in the future.

Document Tags and Contributors

Contributors to this page: chrisdavidmills, Sheppy, mdnwebdocs-bot, jpmedley
Last updated by: chrisdavidmills,