angularjs modal模态框----创建可拖动的指令

//最近项目中需要将angular-ui-bootstrap中用到的弹出框，使之可拖动，由于源文件中没有实现，需要自己实现指令，以下即为该指令，亲测可以实现。
.directive('draggable', ['$document', function($document) {
                return function(scope, element, attr) {
                var startX = , startY = , x = , y = ;
                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);
                }
                };
    }]);

如图：已不在屏幕中央，为拖动后的效果