How to detect DIV's dimension changed?

Question

I\'ve the following sample html, there is a DIV which has 100% width. It contains some elements. While performing windows re-sizing, the inner elements may be re-positioned,

Answer 1

Here is a simplified version of the solution by @nkron, applicable to a single element (instead of an array of elements in @nkron's answer, complexity I did not need).

function onResizeElem(element, callback) {    
  // Save the element we are watching
  onResizeElem.watchedElementData = {
    element: element,
    offsetWidth: element.offsetWidth,
    offsetHeight: element.offsetHeight,
    callback: callback
  };

  onResizeElem.checkForChanges = function() {
    const data = onResizeElem.watchedElementData;
    if (data.element.offsetWidth !== data.offsetWidth || data.element.offsetHeight !== data.offsetHeight) {
      data.offsetWidth = data.element.offsetWidth;
      data.offsetHeight = data.element.offsetHeight;
      data.callback();
    }
  };

  // Listen to the window resize event
  window.addEventListener('resize', onResizeElem.checkForChanges);

  // Listen to the element being checked for width and height changes
  onResizeElem.observer = new MutationObserver(onResizeElem.checkForChanges);
  onResizeElem.observer.observe(document.body, {
    attributes: true,
    childList: true,
    characterData: true,
    subtree: true
  });
}

The event listener and observer can be removed by:

window.removeEventListener('resize', onResizeElem.checkForChanges);
onResizeElem.observer.disconnect();