核心代码如下：
$( 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" ); }); });
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