如何用JavaScript从头开始实现拖放div？

它应该是CSS和JavaScript的组合。应采取的步骤如下：

将其置于所有其他元素之上（要指定哪个属性？）

单击事件时捕获该事件（要侦听哪个事件？）

在鼠标移动时移动div

但是细节是什么呢？

jQuery方式： 查看插件和

实际上，jQuery框架已经投入了数百个小时，使得像这样的复杂任务变得几乎微不足道。利用jQuery团队的努力，让编写丰富的跨浏览器应用程序变得更容易；）

查克·诺里斯的方式： 如果您坚持使用原始javascript尝试此操作。你会想做一些事情。第一，以编程方式将所有可拖动项设置为相对/绝对位置。如果您单击某个特定项目，请使其在CSS中的上/左值反映鼠标的x、y轴所做的更改，直到释放单击为止。此外，您还需要在单击每个拖动表以将其显示在视图中时更新其z索引

教程：

使其绝对定位，具有高z指数

检查div的onmousedown

使用事件的mouseX和mouseY属性移动div

以下是一个来自（更新）的示例：

/**
*Drag.js：拖动绝对定位的HTML元素。
*
*此模块定义一个设计用于调用的drag（）函数
*从onmousedown事件处理程序。随后的mousemove事件将
*移动指定的元素。鼠标悬停事件将终止拖动。
*如果元素被拖离屏幕，则窗口不会滚动。
*此实现可与DOM级别2事件模型和
*IE事件模型。
*
*论据：
*
*elementToDrag：接收mousedown事件或
*一些包含元素。它必须绝对定位。它的
*style.left和style.top值将根据用户的
*拖。
*
*事件：mousedown事件的事件对象。
*
*如何使用此功能的示例：
*       
*      
*      
*      
*      
*拖我
*      
*      
*这是一个测试。测试，测试，测试。这是一个测试。测试。
*      
*
*作者：大卫·弗拉纳根；Javascript：权威指南（O'Reilly）
*页码：422
**/
函数拖动（elementToDrag，事件）
{
//鼠标位置（在窗口坐标中）
//阻力开始的位置
var startX=event.clientX，startY=event.clientY；
//文件的原始位置（在文档坐标中）
//要拖动的元素。因为elementToDrag是
//绝对定位，我们假设其抵销母公司为
//文件bodt。
var origX=elementToDrag.offsetLeft，origY=elementToDrag.offsetTop；
//即使坐标是以不同的方式计算的
//坐标系，我们仍然可以计算它们之间的差异
//并在moveHandler（）函数中使用它
//拖动过程中，滚动条的位置不会改变。
var deltaX=startX-origX，deltaY=startY-origY；
//注册将响应mousemove事件的事件处理程序
//以及此mousedown事件之后的mouseup事件。
if（document.addEventListener）//DOM级别2事件模型
{
//注册捕获事件处理程序
document.addEventListener（“mousemove”，moveHandler，true）；
document.addEventListener（“mouseup”，upHandler，true）；
}
else if（document.attachEvent）//IE 5+事件模型
{
//在IE事件模型中，我们通过调用
//在元素上设置setCapture（）以捕获它们。
elementToDrag.setCapture（）；
elementToDrag.attachEvent（“onmousemove”，moveHandler）；
elementToDrag.attachEvent（“onmouseup”，upHandler）；
//将丢失鼠标捕获视为mouseup事件。
elementToDrag.attachEvent（“onclosecapture”，upHandler）；
}
else//ie4事件模型
{
//在IE 4中，我们不能使用attachEvent（）或setCapture（），因此我们设置
//事件处理程序直接处理文档对象，并希望
//我们需要的鼠标事件将出现。
var oldmovehandler=document.onmousemove；//由upHandler（）使用
var olduphandler=document.onmouseup；
document.onmousemove=moveHandler；
document.onmouseup=upHandler；
}
//我们已经处理了这件事，别让别人看到。
if（event.stoptropagation）event.stoptropagation（）；//DOM级别2
else event.cancelBubble=true；//IE
//现在阻止任何默认操作。
if（event.preventDefault）event.preventDefault（）；//DOM级别2
else event.returnValue=false；//IE
/**
*这是一个处理程序，当元素
*正在拖动。它负责移动元素。
**/
函数moveHandler（e）
{
如果（！e）e=window.event；//IE事件模型
//将元素移动到当前鼠标位置，并根据需要进行调整
//初始鼠标单击的偏移量所需。
elementToDrag.style.left=（e.clientX-deltaX）+“px”；
elementToDrag.style.top=（e.clientY-deltaY）+“px”；
//不要让任何人看到这件事。
if（e.stopPropagation）e.stopPropagation（）；//DOM级别2
else e.cancelBubble=true；//IE
}
/**
*这是捕获最终mouseup事件的处理程序
*在拖动结束时发生。
**/
函数upHandler（e）
{
如果（！e）e=window.event；//IE事件模型
//注销捕获事件处理程序。
如果（文件）
/**
 *  Drag.js:    drag absolutely positioned HTML elements.
 *
 *  This module defines a single drag() function that is designed to be called
 *  from an onmousedown event handler. Subsequent mousemove event will
 *  move the specified element. A mouseup event will terminate the drag.
 *  If the element is dragged off the screen, the window does not scroll.
 *  This implementation works with both the DOM Level 2 event model and the
 *  IE event model.
 *
 *  Arguments:
 *
 *      elementToDrag: the element that received the mousedown event or
 *          some containing element. It must be absolutely positioned. Its
 *          style.left and style.top values will be changed based on the user's
 *          drag.
 *
 *      event: ethe Event object for the mousedown event.
 *
 *  Example of how this can be used:
 *      <script src="Drag.js"></script> <!-- Include the Drag.js script -->
 *      <!-- Define the element to be dragged -->
 *      <div style="postion:absolute; left:100px; top:100px; width:250px;
 *                  background-color: white; border: solid black;">
 *      <!-- Define the "handler" to drag it with. Note the onmousedown attribute. -->
 *      <div style="background-color: gray; border-bottom: dotted black;
 *                  padding: 3px; font-family: sans-serif; font-weight: bold;"
 *          onmousedown="drag(this.parentNode, event);">
 *      Drag Me <!-- The content of the "titlebar" -->
 *      </div>
 *      <!-- Content of the draggable element -->
 *      <p>This is a test. Testing, testing, testing.<p>This is a test.<p>Test.
 *      </div>
 *
 *  Author: David Flanagan; Javascript: The Definitive Guide (O'Reilly)
 *  Page: 422
 **/
 function drag(elementToDrag, event)
 {
     // The mouse position (in window coordinates)
     // at which the drag begins
     var startX = event.clientX, startY = event.clientY;

     // The original position (in document coordinates) of the
     // element that is going to be dragged. Since elementToDrag is
     // absolutely positioned, we assume that its offsetParent is the
     //document bodt.
     var origX = elementToDrag.offsetLeft , origY = elementToDrag.offsetTop;

     // Even though the coordinates are computed in different
     // coordinate systems, we can still compute the difference between them
     // and use it in the moveHandler() function. This works because
     // the scrollbar positoin never changes during the drag.
     var deltaX = startX - origX, deltaY = startY - origY;

     // Register the event handlers that will respond to the mousemove events
     // and the mouseup event that follow this mousedown event.
     if (document.addEventListener) //DOM Level 2 event model
     {
         // Register capturing event handlers
         document.addEventListener("mousemove", moveHandler, true);
         document.addEventListener("mouseup", upHandler, true);
     }
     else if (document.attachEvent) //IE 5+ Event Model
     {
         //In the IE event model, we capture events by calling
         //setCapture() on the element to capture them.
         elementToDrag.setCapture();
         elementToDrag.attachEvent("onmousemove", moveHandler);
         elementToDrag.attachEvent("onmouseup", upHandler);
         // Treat loss of mouse capture as a mouseup event.
         elementToDrag.attachEvent("onclosecapture", upHandler);
     }
     else //IE 4 Event Model
     {
         // In IE 4, we can't use attachEvent() or setCapture(), so we set
         // event handlers directly on the document object and hope that the
         // mouse event we need will bubble up.
         var oldmovehandler = document.onmousemove; //used by upHandler()
         var olduphandler = document.onmouseup;
         document.onmousemove = moveHandler;
         document.onmouseup = upHandler;
     }

     // We've handled this event. Don't let anybody else see it.
     if (event.stopPropagation) event.stopPropagation();    //  DOM Level 2
     else event.cancelBubble = true;                        //  IE

     // Now prevent any default action.
     if (event.preventDefault) event.preventDefault();      //  DOM Level 2
     else event.returnValue = false;                        //  IE

     /**
      * This is the handler that captures mousemove events when an element
      * is being dragged. It is responsible for moving the element.
      **/
      function moveHandler(e)
      {
          if (!e) e = window.event; //  IE Event Model

          // Move the element to the current mouse position, adjusted as
          // necessary by the offset of the initial mouse-click.
          elementToDrag.style.left = (e.clientX - deltaX) + "px";
          elementToDrag.style.top = (e.clientY - deltaY) + "px";

          // And don't let anyone else see this event.
          if (e.stopPropagation) e.stopPropagation();       // DOM Level 2
          else e.cancelBubble = true;                       // IE
      }

      /**
       * This is the handler that captures the final mouseup event that
       * occurs at the end of a drag.
       **/
       function upHandler(e)
       {
           if (!e) e = window.event;    //IE Event Model

           // Unregister the capturing event handlers.
           if (document.removeEventListener) // DOM event model
            {
                document.removeEventListener("mouseup", upHandler, true);
                document.removeEventListener("mousemove", moveHandler, true);
            }
            else if (document.detachEvent)  //  IE 5+ Event Model
            {
                elementToDrag.detachEvent("onlosecapture", upHandler);
                elementToDrag.detachEvent("onmouseup", upHandler);
                elementToDrag.detachEvent("onmousemove", moveHandler);
                elementToDrag.releaseCapture();
            }
            else    //IE 4 Event Model
            {
                //Restore the original handlers, if any
                document.onmouseup = olduphandler;
                document.onmousemove = oldmovehandler;
            }

            //  And don't let the event propagate any further.
            if (e.stopPropagation) e.stopPropagation(); //DOM Level 2
            else e.cancelBubble = true;                 //IE
       }
 }

 function closeMe(elementToClose)
 {
     elementToClose.innerHTML = '';
     elementToClose.style.display = 'none';
 }

 function minimizeMe(elementToMin, maxElement)
 {
     elementToMin.style.display = 'none';
 }

<!DOCTYPE HTML>
<html>
<head>
    <script>
    function allowDrop(ev) {
        ev.preventDefault();
    }

    function drag(ev) {
        ev.dataTransfer.setData("text", ev.target.id);
    }

    function drop(ev) {
        ev.preventDefault();
        var data = ev.dataTransfer.getData("text");
        ev.target.appendChild(document.getElementById(data));
    }
    </script>
    <style>
        .draggable {
            border: 1px solid black;
            width: 30px;
            height: 20px;
            float: left;
            margin-right: 5px;
        }
        #target {
            border: 1px solid black;
            width: 150px;
            height: 100px;
            padding: 5px;
        }
    </style>
</head>
<body>

    <h1>Drag and Drop</h1>

    <h2>Target</h2>
    <div id="target" ondrop="drop(event)" ondragover="allowDrop(event)"></div>

    <h2>Draggable Elements</h2>
    <div id="draggable1" class="draggable" draggable="true" ondragstart="drag(event)"></div>
    <div id="draggable2" class="draggable" draggable="true" ondragstart="drag(event)"></div>
    <div id="draggable3" class="draggable" draggable="true" ondragstart="drag(event)"></div>

</body>
</html>

<body>
    <div id="dragme" draggable="true">Drag Me</div>
    <div id="dropzone">Drop Here</div>
</body>

<script>
    var dragme = document.getElementById('dragme')
    var dropzone = document.getElementById('dropzone')

    dragme.addEventListener('dragstart',function(e){
        dropzone.innerHTML = "drop here"
    })

    dropzone.addEventListener('dragover',function(e){
        e.preventDefault()
    })
    dropzone.addEventListener('drop',function(e){
        e.preventDefault()
        dropzone.innerHTML = "dropped"
    })
</script>

<!DOCTYPE html>
<html lang="en">
  <head>
    <meta charset="UTF-8" />
    <meta name="viewport" content="width=device-width, initial-scale=1.0" />
    <meta http-equiv="X-UA-Compatible" content="ie=edge" />
    <title>Document</title>
    <style>
      body,
      html {
        width: 100%;
        height: 100%;
        padding: 0px;
        margin: 0px;
      }
      #box {
        width: 100px;
        height: 100px;
        margin: auto;
        background-color: lightblue;
      }
      #box:active {
        border: 1px solid black;
        box-shadow: 2px 2px 5px 5px #bbb6b6;
      }
    </style>
  </head>
  <body>
    <div id="box"></div>
  </body>
  <script>
    var box = document.getElementById("box");
    var diff = {};
    var getBoxPos = function() {
      return {
        x: box.getBoundingClientRect().x,
        y: box.getBoundingClientRect().y
      };
    };
    var calcDiff = function(x, y) {
      var boxPos = getBoxPos();
      diff = {
        x: x - boxPos.x,
        y: y - boxPos.y
      };
    };
    var handleMouseMove = function(event) {
      var x = event.x;
      var y = event.y;
      x -= diff.x;
      y -= diff.y;

      console.log("X " + x + " Y " + y);
      box.style.position = "absolute";
      box.style.transform = "translate(" + x + "px ," + y + "px)";
    };

    box.addEventListener("mousedown", function(e) {
      calcDiff(e.x, e.y);
      box.addEventListener("mousemove", handleMouseMove, true);
    });

    box.addEventListener("mouseup", function(e) {
      console.log("onmouseup");
      box.removeEventListener("mousemove", handleMouseMove, true);
    });
  </script>
</html>