javascript - 如何设置可拖动div的起始位置？

Question

我有一个可拖动的 div，只要我不通过 top, right, … CSS 改变它的位置，它就可以正常工作。我的目标是将 div 的预拖动位置设置为其窗口的右上角，我使用 top = 0, right = 0;问题是，div 会固定在那个位置并且 stretches拖动时。

dragElement(document.getElementById("myModal"));

function dragElement(elmnt) {
  var pos1 = 0, pos2 = 0, pos3 = 0, pos4 = 0;
  if (document.getElementById(elmnt.id + "header")) {
  document.getElementById(elmnt.id + "header").onmousedown = dragMouseDown;} 
  else {elmnt.onmousedown = dragMouseDown;}

  function dragMouseDown(w) {
    w = w || window.event;
    w.preventDefault();
    pos3 = w.clientX;
    pos4 = w.clientY;
    document.onmouseup = closeDragElement;
    document.onmousemove = elementDrag;}
    
  function elementDrag(w) {
    w = w || window.event;
    w.preventDefault();
    pos1 = pos3 - w.clientX;
    pos2 = pos4 - w.clientY;
    pos3 = w.clientX;
    pos4 = w.clientY;
    elmnt.style.top = (elmnt.offsetTop - pos2) + "px";
    elmnt.style.left = (elmnt.offsetLeft - pos1) + "px";}

  function closeDragElement() {
    document.onmouseup = null;
    document.onmousemove = null;}}

#myModal {
    position: absolute;
    z-index: 9;
    background-color: #f1f1f1;
    text-align: center;
    border: 1px solid #d3d3d3;
    top: 0;
    right: 0;}
#myModalheader {
    padding: 10px;
    cursor: move;
    z-index: 10;
    background-color: #2196F3;
    color: #fff;}

<div id="myModal">
  <div id="myModalheader">Click here to move</div>
  <p>Move</p><p>this</p><p>DIV</p>
</div>

有什么解决方法吗？感谢您的帮助。

Answer 1

给元素一个宽度和高度，你应该很好。

dragElement(document.getElementById("myModal"));

function dragElement(elmnt) {
  var pos1 = 0, pos2 = 0, pos3 = 0, pos4 = 0;
  if (document.getElementById(elmnt.id + "header")) {
  document.getElementById(elmnt.id + "header").onmousedown = dragMouseDown;} 
  else {elmnt.onmousedown = dragMouseDown;}

  function dragMouseDown(w) {
    w = w || window.event;
    w.preventDefault();
    pos3 = w.clientX;
    pos4 = w.clientY;
    document.onmouseup = closeDragElement;
    document.onmousemove = elementDrag;}
    
  function elementDrag(w) {
    w = w || window.event;
    w.preventDefault();
    pos1 = pos3 - w.clientX;
    pos2 = pos4 - w.clientY;
    pos3 = w.clientX;
    pos4 = w.clientY;
    elmnt.style.top = (elmnt.offsetTop - pos2) + "px";
    elmnt.style.left = (elmnt.offsetLeft - pos1) + "px";}

  function closeDragElement() {
    document.onmouseup = null;
    document.onmousemove = null;}}

#myModal {
    position: absolute;
    z-index: 9; height: 200px; width: 200px;
    background-color: #f1f1f1;
    text-align: center;
    border: 1px solid #d3d3d3;
    top: 0;
    right: 0;}
#myModalheader {
    padding: 10px;
    cursor: move;
    z-index: 10;
    background-color: #2196F3;
    color: #fff;}

<div id="myModal">
  <div id="myModalheader">Click here to move</div>
  <p>Move</p><p>this</p><p>DIV</p>
</div>