[Jquery]导航菜单效果-纵向

$( document ).ready( function(e){

var $catCont = $( ".cat-cont" );    //二级菜单div
    var $catList = $( ".J_Cat" );       //一级菜单li

$catList.on( "mouseenter", function(){

var index = $( this ).index();
        var $curCatList = $( ".cat-cont-bd>li:eq(" + index + ")" );         //鼠标移上去对应的二级菜单的li

$catList.removeClass( "selected selected-prev" );

$( this ).addClass( "selected" ).prev().addClass( "selected-prev" );

$catCont.show();

$curCatList.css( "display", "list-item").siblings().css( "display", "none" );

var viewHeight = $( window ).height();
        var catOffsetTop = $( this ).offset().top - $( window ).scrollTop();
        var catBottomGap = viewHeight - catOffsetTop;

var catPositionTop = $( this ).position().top;

var catContHeight = $catCont.height();

if( catBottomGap >= catContHeight ) {
            $catCont.css( "top", catPositionTop );
        }
        if( catBottomGap < catContHeight && viewHeight >= catContHeight ) {
            $catCont.css( "top", catPositionTop - ( catContHeight - catBottomGap ) - 20 );
        }
        if( catBottomGap < catContHeight && viewHeight < catContHeight ) {
            $catCont.css( "top", catPositionTop );
        }
        if( catBottomGap <= 66 ) {
            $catCont.css( "top", catPositionTop - catContHeight + 33 );
        }

}).on( "mouseleave", function( event ){
        if( !$( event.relatedTarget ).hasClass( "cat-cont-bd" ) ){    //交互灾难:离开一级菜单划不到二级菜单，如何知道离开一级菜单后进入的是二级菜单？jquery提供属性：event.relatedTarget(离开后进入的对象)
            $( this ).removeClass( "selected selected-prev" );
            $catCont.hide();
        }
    });

$catCont.on( "mouseleave", function(){
        $catCont.hide();
        $catList.removeClass( "selected selected-prev" );
    });
});