android连续拖动导致挂起的解决方法

(function () {  var canvas = new fabric.Canvas('canvas');  var canvas_el = document.getElementById('canvas');  var canvas1 = new fabric.Canvas('canvas1');  var group;  fabric.Image.fromURL('img/blank.png', function (img) {    var img1 = img.set({      left: 0,      top: 0    });    fabric.Image.fromURL('img/blank.png', function (img) {      var img2 = img.set({        left: 0,        top: 0      });      group = new fabric.Group([img1, img2], {        left: 0,        top: 0      });      canvas.add(group)    });  });  fabric.Image.fromURL('img/blank.png', function (img) {    var img1 = img.set({      left: 0,      top: 0    });    fabric.Image.fromURL('img/blank.png', function (img) {      var img2 = img.set({        left: 0,        top: 0      });      group1 = new fabric.Group([img1, img2], {        left: 0,        top: 0      });      canvas1.add(group1)    });  });  $(document).ready(function () {    /* Define drag and drop zones */    var $drop = $('#canvas-drop-area,#canvas-drop-area1'),      $gallery = $('td > #image-list li'),      $draggedImage=null;    /* Define the draggable properties */    $gallery.draggable({       helper: 'clone',      start: function (e) {      $draggedImage=event.target;        $drop.css({          'display': 'block'        })      },      stop: function () {        $(this).find('img').css({          /* 'opacity': 0.4 */        });        $drop.css({          'display': 'none'        });        $draggedImage=null;      },      revert: true    });    /* Define the events for droppable properties */    $drop.droppable({      over: function (event, ui) {        $(this).addClass('active');      },      drop: function (event, ui) {        var image =$draggedImage&& $draggedImage.src;        console.log($draggedImage.alt);        img_to_canvas(image,$draggedImage.alt,$(event.target).is("#canvas-drop-area")?1:2);      },      out: function (event, ui) {        $(this).removeClass('active');      },      deactivate: function (event, ui) {        $(this).removeClass('active');      }    });  });  var img_to_canvas = function(image,sendfront,checkcanvas) {    var img = new Image();    img.src = image;    if(checkcanvas =='1'){      if(sendfront=='top'){        fabric.util.loadImage(img.src, function (img) {          group.item(0).setElement(img);            canvas.renderAll();        });       }else{        fabric.util.loadImage(img.src, function (img) {          group.item(1).setElement(img);            canvas.renderAll();        });       }      canvas.calcOffset();     }else{      if(sendfront=='top'){        fabric.util.loadImage(img.src, function (img) {          group1.item(0).setElement(img);            canvas1.renderAll();        });           }else{        fabric.util.loadImage(img.src, function (img) {          group1.item(1).setElement(img);            canvas1.renderAll();        });       }      canvas1.calcOffset();        }  }})();

$drop.droppable({  over: function (event, ui) {    $(this).addClass('active');  },  drop: function (event, ui) {    var image =$draggedImage&& $draggedImage.src;

$drop.droppable({    over: function(event, ui) {      $(this).addClass('active');    },    drop: function(event, ui) {      $draggedImage = ui.draggable.find("img").get(0);