SOURCE

let div=document.getElementById("dsa")
let diffx=0,diffy=0,falg=false;
div.onmousedown=function(e){
  diffx=e.offsetX;
  diffy=e.offsetY;
  flag=true;
}
div.onmousemove=function(e){
  if(flag){
  div.style.marginLeft=(e.clientX-diffx)+"px";
  div.style.marginTop=(e.clientY-diffy)+"px";
  }
}

div.onmouseup=function(){
  flag=false;
}

<div id="dsa"></div>

div{

  height:100px;
  width:100px;
  background:green;
}