<div>Not positioned</div>
<div class="absolute">Absolute</div>
<p>Lorem ipsum dolor sit amet consectetur adipisicing elit. Explicabo aliquid quibusdam in! Magni ratione minus, quaerat iure repellat ipsam, culpa voluptas incidunt molestias fuga voluptates! Provident velit nam unde veniam.</p><p>Lorem ipsum dolor sit amet consectetur adipisicing elit. Explicabo aliquid quibusdam in! Magni ratione 
<div class="float">Float Left</div>  
  minus, quaerat iure repellat ipsam, culpa voluptas incidunt molestias fuga voluptates! Provident velit nam unde veniam.</p><p>Lorem ipsum dolor sit amet consectetur adipisicing elit. Explicabo aliquid quibusdam in! Magni ratione minus, quaerat iure repellat ipsam, culpa voluptas incidunt molestias fuga voluptates! Provident velit nam unde veniam.</p>
<output></output>

body {font-family: helvetica, arial, sans-serif;}
div {
  cursor: crosshair;
  width: 10vw;
  height: 4em;
  background: #369;
  color: white;
  text-align: center;
  display: block;
}
div.absolute {
  position: absolute;
  top: 0;
  right: 0;
}
div.float {
  float: left;
  margin: 10px;
}
output {
  position: fixed;
  top: 0;
  left: calc(50% - 5vw);
  display: block;
  background: #ccc;
  height: 1.5em;
  padding: 1vh 1vw;
  line-height: 1.5em;
}

const out = document.querySelector('output');
const plaindiv = document.querySelector('div');
const absdiv = document.querySelector('div.absolute');
const floatdiv = document.querySelector('div.float');

const getposition = ev => {
    let x = ev.clientX;
    let y = ev.clientY;
    let pos = ev.target.getBoundingClientRect();
    return {
      x: x - pos.x|0,
      y: y - pos.y|0
    };
  }
 
 const showposition = ev => {
   let {x:x,y:y} = getposition(ev);
   out.innerText = `x: ${x} y: ${y}`;
 };
plaindiv.addEventListener('mousemove', showposition);
absdiv.addEventListener('mousemove', showposition);
floatdiv.addEventListener('mousemove', showposition);