1. function drag(obj) {
    2.         obj.onmousedown = function (event) {
    3.             obj.capture && obj.capture();
    4.             let left = event.clientX;
    5.             let top = event.clientY;
    6.             let offsetX = left - obj.offsetLeft;
    7.             let offsetY = top - obj.offsetTop;
    9.             document.onmousemove = function (event) {
    10.                 let left = event.clientX;
    11.                 let top = event.clientY;
    12.                 obj.style.left = `${left - offsetX}.px`;
    13.                 obj.style.top = `${top - offsetY}.px`;
    14.             }
    16.             document.onmouseup = function (){
    17.                 document.onmousemove = null;
    18.                 document.onmouseup = null;
    19.                 obj.releaseCapture && obj.releaseCapture();
    20.             }
    21.             return false;
    22.         }
    23.     }