The bottom, left, right, and top properties are what you would expect from the result of element.getBoundingClientRect(). naturalHeight and naturalWidth are properties that are native to img elements, and for all non-img elements they are coalesced with scrollHeight and scrollWidth, respectively. These properties are retrieved on mount, but will also automatically update if the element is resized thanks to ResizeObserver. Please note that elements that do not support content (such as img) are not supported by this resize listener because there is no content box to observe. If you need to support those elements, simply create a higher-order component that wraps that element in a div and decorate that component.