MouseEvent: layerY property

<p>To display the mouse coordinates please click anywhere on the page.</p>
<div id="d1">
  <span>
    This is an un-positioned div so clicking it will return layerX/layerY values
    almost the same as pageX/PageY values.
  </span>
</div>
<div id="d2">
  <span>
    This is a positioned div so clicking it will return layerX/layerY values
    that are relative to the top-left corner of this positioned element. Note
    the pageX\pageY properties still return the absolute position in the
    document, including page scrolling.
  </span>
  <span>
    Make the page scroll more! This is a positioned div so clicking it will
    return layerX/layerY values that are relative to the top-left corner of this
    positioned element. Note the pageX\pageY properties still return the
    absolute position in the document, including page scrolling.
  </span>
</div>
<div id="d3">
  <form name="form_coords" id="form1">
    Parent Element id: <input type="text" name="parentId" size="7" /><br />
    pageX: <input type="text" name="pageXCoords" size="7" /> pageY:
    <input type="text" name="pageYCoords" size="7" /><br />
    layerX: <input type="text" name="layerXCoords" size="7" /> layerY:
    <input type="text" name="layerYCoords" size="7" />
  </form>
</div>

#d1 {
  border: solid blue 1px;
  padding: 20px;
}
#d2 {
  position: absolute;
  top: 180px;
  left: 80%;
  right: auto;
  width: 40%;
  border: solid blue 1px;
  padding: 20px;
}
#d3 {
  position: absolute;
  top: 240px;
  left: 20%;
  width: 50%;
  border: solid blue 1px;
  padding: 10px;
}

function showCoords(evt) {
  const form = document.forms.form_coords;
  const parentId = evt.target.parentNode.id;
  form.parentId.value = parentId;
  form.pageXCoords.value = evt.pageX;
  form.pageYCoords.value = evt.pageY;
  form.layerXCoords.value = evt.layerX;
  form.layerYCoords.value = evt.layerY;
}
window.addEventListener("mousedown", showCoords);