html5rocks.com/en/tutorials/dnd/basics/

1. dragstart
2. drag
3. dragenter
4. dragleave
5. dragover
6. drop
7. dragend

(...)

function move_start(e) {
  e.preventDefault();
}
function move_drag_over(e) {
  e.preventDefault(); // preventing quircky behaviour
}
function moveDrop(e) {
  e.preventDefault();
  which_art.style.left = e.pageX - my_x + 'px';
  which_art.style.top = e.pageY - my_y + 'px';
}

(...)
document.querySelector("body").addEventListener("dragstart", move_start, false);
document.querySelector("body").addEventListener("dragover", move_drag_over, false);
document.querySelector("body").addEventListener("drop", move_drop, false);