.demo {

  margin: 100px auto;

  width: 200px;

  height: 200px;

  background-color: #55ffff;

}

​

var div = document.querySelector(".demo");

div.addEventListener("mousemove", function (e) {

  var x = e.pageX - div.offsetLeft;

  var y = e.pageY - div.offsetTop;

  div.innerHTML = "x 坐标为：" + x + "<br> y 坐标为：" + y;

});

​