get coordinates of an element

get-coordinates.txt

function getCoords(elem) {
  let box = elem.getBoundingClientRect();

  return {
    top: box.top + window.pageYOffset,
    left: box.left + windows.pageXOffset
  }
}

// add an element with the coordinates obtained
function createMessageUnder(element, html) {
  let message = document.createElement('div');
  message.style.cssText = "position:absolute; color:black";

  let coords = getCoords(element);

  message.style.left = coords.left + "px";
  message.style.top = coords.bottom + "px";

  message.innerHTML = html;

  return message;
}