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ResizeObserverEntry

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.devicePixelContentBoxSize Read only

An object containing the new content box size in device pixels 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

Browser compatibility

Desktop Mobile
Chrome Edge Firefox Internet Explorer Opera Safari WebView Android Chrome Android Firefox for Android Opera Android Safari on IOS Samsung Internet
ResizeObserverEntry
64
79
69
No
51
13.1
64
64
79
47
13.4
9.0
borderBoxSize
84
84
92
69-92
Implemented as a single object representing a content box size, rather than an array of content box size objects.
No
70
15.4
84
84
92
79-92
Implemented as a single object representing a content box size, rather than an array of content box size objects.
60
15.4
14.0
contentBoxSize
84
84
92
69-92
Implemented as a single object representing a content box size, rather than an array of content box size objects.
No
70
15.4
84
84
92
79-92
Implemented as a single object representing a content box size, rather than an array of content box size objects.
60
15.4
14.0
contentRect
64
79
69
No
51
13.1
64
64
79
47
13.4
9.0
devicePixelContentBoxSize
84
84
93
No
70
No
84
84
93
60
No
14.0
target
64
79
69
No
51
13.1
64
64
79
47
13.4
9.0

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Licensed under the Creative Commons Attribution-ShareAlike License v2.5 or later.
https://developer.mozilla.org/en-US/docs/Web/API/ResizeObserverEntry