angularjs创建弹出框实现拖动效果

.directive('draggable', ['$document', function($document) {
        return function(scope, element, attr) {
        var startX = 0, startY = 0, x = 0, y = 0;
        element= angular.element(document.getElementsByClassName("modal-dialog")); 
        element.css({
          position: 'relative',
          cursor: 'move'
        });
 
        element.on('mousedown', function(event) {
          // Prevent default dragging of selected content
          event.preventDefault();
          startX = event.pageX - x;
          startY = event.pageY - y;
          $document.on('mousemove', mousemove);
          $document.on('mouseup', mouseup);
        });
 
        function mousemove(event) {
          y = event.pageY - startY;
          x = event.pageX - startX;
          element.css({
          top: y + 'px',
          left: x + 'px'
          });
        }
 
        function mouseup() {
          $document.off('mousemove', mousemove);
          $document.off('mouseup', mouseup);
        }
        };
  }]);