javascript实现拖动元素交换位置

body,ul,li{margin:0;padding:0;}
ul{list-style: none;}
body{font:13px/1.5 Tahoma;}
#box{position:relative;width:435px;height:580px;margin:10px auto;padding: 10px 5px 10px 10px;border: 1px solid #ccc;}
#box li{float:left;width:80px;height:188px;overflow:hidden;background: #ccc;border: 1px solid #999;}
#box li.hig{width:78px;height:186px;overflow:hidden;border:2px dashed blue;} 

<ul id="box"></ul>

var zIndex = 1;
window.onload = function() {

  var oBox = document.getElementById("box");
  var aLi = oBox.getElementsByTagName("li");
  var aPos = [];
  var aData = [];
  for (i = 0; i < 15; i++)aData.push(i+1);


  //插入结构
  var oFragment = document.createDocumentFragment();
  for (i = 0; i < aData.length; i++) {
    var oLi = document.createElement("li");
    oFragment.appendChild(oLi)
  }
  oBox.appendChild(oFragment);

  //布局转换
  for (i = 0; i < aLi.length; i++) {
    aLi[i].index = i;
    aLi[i].style.top = aLi[i].offsetTop + "px";
    aLi[i].style.left = aLi[i].offsetLeft + "px";
    aLi[i].style.margin = "0 5px 5px 0";
    aPos.push({
      "left": aLi[i].offsetLeft,
      "top": aLi[i].offsetTop
    })
  }
  for (i = 0; i < aLi.length; i++) {
    aLi[i].style.position = "absolute";    
    drag(aLi[i])
  }

  //拖拽函数
  function drag(obj, handle) {
    var handle = handle || obj;
    handle.style.cursor = "move";
    handle.onmousedown = function(event) {
      var event = event || window.event;
      var disX = event.clientX - this.offsetLeft;
      var disY = event.clientY - this.offsetTop;
      var oNear = null;
      obj.style.zIndex = zIndex++;
      document.onmousemove = function(event) {
        var event = event || window.event;
        var iL = event.clientX - disX;
        var iT = event.clientY - disY;
        var maxL = obj.parentNode.clientWidth - obj.offsetWidth;
        var maxT = obj.parentNode.clientHeight - obj.offsetHeight;

        iL < 0 && (iL = 0);
        iT < 0 && (iT = 0);
        iL > maxL && (iL = maxL);
        iT > maxT && (iT = maxT);
        obj.style.left = iL + "px";
        obj.style.top = iT + "px";

        for (i = 0; i < aLi.length; i++) aLi[i].className = "";

        oNear = findNearest(obj);

        oNear && (oNear.className = "hig");

        return false
      };
      document.onmouseup = function() {
        document.onmousemove = null;
        document.onmouseup = null;
        if (oNear) {
          var tIndex = obj.index;
          obj.index = oNear.index;
          oNear.index = tIndex;
          startMove(obj, aPos[obj.index]);
          startMove(oNear, aPos[oNear.index], function() {
            
          });
          oNear.className = "";
        } else {
          startMove(obj, aPos[obj.index])
        }
        handle.releaseCapture && handle.releaseCapture()
      };
      this.setCapture && this.setCapture();
      return false
    }
  }

  //找出相遇点中最近的元素
  function findNearest(obj) {
    var filterLi = [];
    var aDistance = [];

    for (i = 0; i < aLi.length; i++) aLi[i] != obj && (isButt(obj, aLi[i]) && (aDistance.push(getDistance(obj, aLi[i])), filterLi.push(aLi[i])));

    var minNum = Number.MAX_VALUE;
    var minLi = null;

    for (i = 0; i < aDistance.length; i++) aDistance[i] < minNum && (minNum = aDistance[i], minLi = filterLi[i]);

    return minLi
  }



};
//求两点之间的距离
function getDistance(obj1, obj2) {
  var a = (obj1.offsetLeft + obj1.offsetWidth / 2) - (obj2.offsetLeft + obj2.offsetWidth / 2);
  var b = (obj1.offsetTop + obj1.offsetHeight / 2) - (obj2.offsetTop + obj2.offsetHeight / 2);
  return Math.sqrt(a * a + b * b)
}

//碰撞检测
function isButt(obj1, obj2) {
  var l1 = obj1.offsetLeft;
  var t1 = obj1.offsetTop;
  var r1 = obj1.offsetLeft + obj1.offsetWidth;
  var b1 = obj1.offsetTop + obj1.offsetHeight;

  var l2 = obj2.offsetLeft;
  var t2 = obj2.offsetTop;
  var r2 = obj2.offsetLeft + obj2.offsetWidth;
  var b2 = obj2.offsetTop + obj2.offsetHeight;

  return !(r1 < l2 || b1 < t2 || r2 < l1 || b2 < t1)
}

//获取最终样式
function getStyle(obj, attr) {
  return parseFloat(obj.currentStyle ? obj.currentStyle[attr] : getComputedStyle(obj, null)[attr])
}

//运动框架
function startMove(obj, pos, onEnd) {
  clearInterval(obj.timer);
  obj.timer = setInterval(function() {
    doMove(obj, pos, onEnd)
  }, 30)
}

function doMove(obj, pos, onEnd) {
  var iCurL = getStyle(obj, "left");
  var iCurT = getStyle(obj, "top");
  var iSpeedL = (pos.left - iCurL) / 5;
  var iSpeedT = (pos.top - iCurT) / 5;
  iSpeedL = iSpeedL > 0 ? Math.ceil(iSpeedL) : Math.floor(iSpeedL);
  iSpeedT = iSpeedT > 0 ? Math.ceil(iSpeedT) : Math.floor(iSpeedT);
  if (pos.left == iCurL && pos.top == iCurT) {
    clearInterval(obj.timer);
    onEnd && onEnd()
  } else {
    obj.style.left = iCurL + iSpeedL + "px";
    obj.style.top = iCurT + iSpeedT + "px";
  }
}