如果在验证后我决定将元素移回？如何设置jquery-ui draggable revert为true？

我正在寻找一种方法来触发事件从恢复状态,如果某些事情没有验证,例如,如果元素存在,它将从另一个列表创建它,但如果它已经存在,它应该转到else并将元素返回到它原来的位置：

$( "#catalog ul" ).droppable({
        tolerance: 'fit',activeClass: "ui-state-default",hoverClass: "ui-state-hover",accept: ":not(.ui-sortable-Helper)",drop: function( event,ui ) {
            //check if already exists
            if($(this).find("#"+$(ui.draggablE).attr("id")).length==0){
                $( "<li id="+$(ui.draggablE).attr("id")+"></li>" ).text( ui.draggable.text() ).appendTo( this )
                .draggable({
                    revert: 'invalid',stop: function(){
                        $(this).draggable('option','revert','invalid');
                    }
                }).droppable({
                    greedy: true,tolerance: 'touch',drop: function(event,ui){
                        ui.draggable.draggable('option',truE);
                    }
                });
            }else{
                //want to make the object go BACk by setTing true to revert
                return false;
            }
        }
    })

ui.draggable.draggable('option',truE);