Notify when element size is changed

const foo = document.getElementById("foo");

const observer = new ResizeObserver((entries) => {
  for (let entry of entries) {
    const cr = entry.contentRect;
    console.log = `Size: ${cr.width}px X ${cr.height}px`;
  }
});
observer.observe(foo);

Source

https://github.com/roeib/JavaScript-snippets#notify-when-element-size-is-changed