<script type="text/javascript">
 //鼠标按下时的X Y坐标
 var mouseDownX;
 var mouseDownY;
 //鼠标按下时移动的X Y 坐标
 var mouseMoveX;
 var mouseMoveY;
 //移动的状态
 var isMove = false;
 /*初始化 选择框 */
 function init() {
  $("#selected").css("display", "none");
  $("#selected").css("top", "0");
  $("#selected").css("left", "0");
  $("#selected").css("width", "0");
  $("#selected").css("height", "0");
 }
 $(document).ready(function() {
  init();
  var selectedTD = new Array();//创建被选中表格数组
  var TD = $("td");//获取所有表格信息
  for ( var i = 0; i < TD.length; i++) {
   selectedTD.push(TD[i]);
  }
  $("#tableDiv").mousedown(function(event) {
   mouseDownX = event.clientX - $(this).offset().left;;
   mouseDownY = event.clientY - $(this).offset().top;
   console.log("mouseDownX=" + mouseDownX +" mouseDownY=" + mouseDownY );
   if(event.target.id.match(/selected/)) {
    isMove = true;
   }
   //鼠标按下并移动时进行判断（拖拽 or 画框）
   $("#tableDiv").mousemove(function(event) {
    mouseMoveX = event.clientX - $(this).offset().left;
    mouseMoveY = event.clientY - $(this).offset().top;
    var selectDiv = document.getElementById("selected");
    if (isMove) {
     //拖拽的代码，因为实在不想算 xy 了，所以使用了jquery ui
     $("#selected").draggable();
     //这部分是负责画框的时候，实时把框住的表格变色的，（代码和下面的代码重复了）
     var left = selectDiv.offsetLeft, top = selectDiv.offsetTop; width = selectDiv.offsetWidth, height = selectDiv.offsetHeight;
     for ( var i = 0; i < selectedTD.length; i++) {
      var sl = selectedTD[i].offsetWidth + selectedTD[i].offsetLeft;
      var st = selectedTD[i].offsetHeight + selectedTD[i].offsetTop;
      if (sl > left && st > top && selectedTD[i].offsetLeft < left + width && selectedTD[i].offsetTop < top + height) {
       if (selectedTD[i].className.indexOf("selected") == -1) {
        selectedTD[i].className = "selected";
       }
      } else { 
       if (selectedTD[i].className.indexOf("selected") != -1) { 
        selectedTD[i].className = "TD"; 
       }
      }
     }
    } else {
     //重复的代码，完了再把它抽取出来
     var left = selectDiv.offsetLeft, top = selectDiv.offsetTop; width = selectDiv.offsetWidth, height = selectDiv.offsetHeight;
     for ( var i = 0; i < selectedTD.length; i++) {
      var sl = selectedTD[i].offsetWidth + selectedTD[i].offsetLeft;
      var st = selectedTD[i].offsetHeight + selectedTD[i].offsetTop;
      if (sl > left && st > top && selectedTD[i].offsetLeft < left + width && selectedTD[i].offsetTop < top + height) {
       if (selectedTD[i].className.indexOf("selected") == -1) {
        selectedTD[i].className = "selected";
       }
      } else {
       if (selectedTD[i].className.indexOf("selected") != -1) { 
        selectedTD[i].className = "TD"; 
       }
      }
     }
     //鼠标抬起结束画框，和拖动
     $("#tableDiv").mouseup(function() {
      console.log("mouseUpX=" + mouseMoveX + " mouseUpY=" + mouseMoveX);
      isMove = false;
      $(this).unbind('mousemove');
     })
     //画框
     displaySelected(mouseDownY, mouseDownX, mouseMoveX, mouseMoveY);
    }
   })
  })
  //当鼠标在已经画好的框上时，改变鼠标指针样式，就是十字形了
  $("#selected").mouseenter(function() {
   $("#selected").css("cursor", "move");
  });
 });
 function displaySelected(mouseDownY, mouseDownX, mouseUpX, mouseUpY) {
  $("#selected").css("display", "block");
  $("#selected").css("top", mouseDownY);
  $("#selected").css("left", mouseDownX);
  var moveX = mouseMoveX - mouseDownX;
  var moveY = mouseMoveY - mouseDownY;
  if (moveY < 0) {
    $("#selected").css("top", event.clientY - $("#table").offset().top);
  }
  if (moveX < 0) {
   $("#selected").css("left", event.clientX - $("#table").offset().left);
  }
  $("#selected").css("width", Math.abs(moveX));
  $("#selected").css("height", Math.abs(moveY));
 }
 </script>

<div id="tableDiv" style="width: 1500px; height: 1500px;top: 100px; left:100px; position: absolute;">
  <div id="selected" style="border:5px dotted rgb(239, 37, 17);position: absolute;display: none;"></div>
  <table border="1" style=" width: 1500px; height: 1500px;" id="table">
  <tr>
   <td id="1" class="TD"></td>
   <td id="2" class="TD"></td>
   <td id="3" class="TD"></td>
   <td id="4" class="TD"></td>
   <td id="5" class="TD"></td>
   <td id="6" class="TD"></td>
  </tr>
  <tr>
   <td id="7" class="TD"></td>
   <td id="8" class="TD"></td>
   <td id="9" class="TD"></td>
   <td id="10" class="TD"></td>
   <td id="11" class="TD"></td>
   <td id="12" class="TD"></td>
  </tr>
  <tr>
   <td id="1" class="TD"></td>
   <td id="2" class="TD"></td>
   <td id="3" class="TD"></td>
   <td id="4" class="TD"></td>
   <td id="5" class="TD"></td>
   <td id="6" class="TD"></td>
  </tr>
  </table>
 <!--表格代码太多所以...-->
 </div>