：JavaScript 设置 DIV 可拖动

<h1>拖动 DIV 元素</h1>


<p>点击以下方框，通过拖动鼠标来拖动元素。</p>


<div id="mydiv">
    <div id="mydivheader">----点我移动----</div>
    <p>Move</p>
    <p>this</p>
    <p>DIV</p>
</div>
<style>
    #mydiv {
        position: absolute;
        z-index: 9;
        background-color: #f1f1f1;
        text-align: center;
        border: 1px solid #d3d3d3;
    }
    
    #mydivheader {
        padding: 10px;
        cursor: move;
        z-index: 10;
        background-color: #2196F3;
        color: #fff;
    }
</style>


<script>
    //Make the DIV element draggagle:
    dragElement(document.getElementById(("mydiv")));
    
    function dragElement(elmnt) {
      var pos1 = 0, pos2 = 0, pos3 = 0, pos4 = 0;
      if (document.getElementById(elmnt.id + "header")) {
        /* if present, the header is where you move the DIV from:*/
        document.getElementById(elmnt.id + "header").onmousedown = dragMouseDown;
      } else {
        /* otherwise, move the DIV from anywhere inside the DIV:*/
        elmnt.onmousedown = dragMouseDown;
      }
    
      function dragMouseDown(e) {
        e = e || window.event;
        // get the mouse cursor position at startup:
        pos3 = e.clientX;
        pos4 = e.clientY;
        document.onmouseup = closeDragElement;
        // call a function whenever the cursor moves:
        document.onmousemove = elementDrag;
      }
    
      function elementDrag(e) {
        e = e || window.event;
        // calculate the new cursor position:
        pos1 = pos3 - e.clientX;
        pos2 = pos4 - e.clientY;
        pos3 = e.clientX;
        pos4 = e.clientY;
        // set the element's new position:
        elmnt.style.top = (elmnt.offsetTop - pos2) + "px";
        elmnt.style.left = (elmnt.offsetLeft - pos1) + "px";
      }
    
      function closeDragElement() {
        /* stop moving when mouse button is released:*/
        document.onmouseup = null;
        document.onmousemove = null;
      }
    }
</script>

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