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);
    }
    };
 }]);