get top of an element JS

  var testDiv = document.getElementById("test");
document.getElementById("demo").innerHTML = testDiv.offsetTop; 

function offset(el) {    var rect = el.getBoundingClientRect(),    scrollLeft = window.pageXOffset || document.documentElement.scrollLeft,    scrollTop = window.pageYOffset || document.documentElement.scrollTop;    return { top: rect.top + scrollTop, left: rect.left + scrollLeft }}
// example usevar div = document.querySelector('div');var divOffset = offset(div);console.log(divOffset.left, divOffset.top);