The target read-only property of the ResizeObserverEntry interface returns a reference to the Element or SVGElement that is being observed.


var element =;
var svgElement =;


An Element or SVGElement representing the element being observed.


The following snippet is taken from the resize-observer-border-radius.html (see source) example. This example includes a green box, sized as a percentage of the viewport size. When the viewport size is changed, the box's rounded corners change in proportion to the size of the box. We could just implement this using border-radius with a percentage, but that quickly leads to ugly-looking elliptical corners; this solution gives you nice square corners that scale with the box size.

To grab a reference to the observed element so we can update its border-radius value after each change, we make use of the target property of each entry —

const resizeObserver = new ResizeObserver(entries => {
  for (let entry of entries) {
    if(entry.contentBoxSize) { = Math.min(100, (entry.contentBoxSize.inlineSize/10) +
                                                      (entry.contentBoxSize.blockSize/10)) + 'px';
    } else { = Math.min(100, (entry.contentRect.width/10) +
                                                      (entry.contentRect.height/10)) + 'px';



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

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