最近有项目要实现N级菜单,首先从布局入手,即判断是否有下级菜单,具体实现代码,大家可以参考下本文
需求分析
简单的分析一下,要实现N级菜单,首先从布局入手,即判断是否有下级菜单
1.没有下一级菜单,直接排列
2.有下级菜单,又分为下级菜单排放位置,和在上级菜单显示类似 '>' 的符号,效果如图:
图:1
初步实现
1.实现是否存在 >
注意: 下面凡是担忧 xxx===yyy ? xxx : xxx都是利用三元表达式,来表达思路。
HTML结构如下:
图:2
•要实现图一的效果,我们只需要判断li标签里面的children.length===2 ? 'span存在' : 'span移除'
2.下级菜单出现位置
HTML结构如下:
•实现这一需求,也需要判断children.length===2 ? '上级菜单相对定位, top为0,left为上级的offsetWidth,下级菜单绝对定位' : '不做任何处理'
具体代码即实现
效果图如下:
代码如下:
<!DOCTYPE html> <html lang="en"> <head> <meta charset="UTF-8"> <title>Document</title> <style type="text/css"> * { margin: 0; padding: 0; } #box { margin: 200px 0 0 50px; text-align: center; color: #ccc; } ul { list-style: none; float: left; } li { width: 150px; height: 40px; line-height: 40px; background-color: #124520; border: 1px solid #eee; position: relative; } li span { position: absolute; top: 0; right: 10px; } li:hover { background-color: #666; transition: background-color .5s; } ul { display: none; } ul.first { display: block; } .relative { position:relative; top: 0; left: 0; } .absolute { position: absolute; left: 0; top: 0; } .show { display: block; } .hide { display: none; } </style> </head> <body> <p id="box"> <ul class="first"> <li>一级菜单 <span>></span> </li> <li>一级菜单 <span>></span> <ul> <li>二级菜单 <span>></span> <ul> <li>三级菜单 <span>></span> </li> <li>三级菜单 <span>></span> </li> <li>三级菜单 <span>></span> </li> <li>三级菜单 <span>></span> </li> </ul> </li> <li>二级菜单 <span>></span> <ul> <li>三级菜单 <span>></span> </li> <li>三级菜单 <span>></span> </li> <li>三级菜单 <span>></span> </li> <li>三级菜单 <span>></span> </li> </ul> </li> <li>二级菜单 <span>></span> </li> <li>二级菜单 <span>></span> <ul> <li>三级菜单 <span>></span> </li> <li>三级菜单 <span>></span> </li> <li>三级菜单 <span>></span> </li> <li>三级菜单 <span>></span> </li> </ul> </li> </ul> </li> <li>一级菜单 <span>></span> <ul> <li>二级菜单 <span>></span> </li> <li>二级菜单 <span>></span> <ul> <li>三级菜单 <span>></span> </li> <li>三级菜单 <span>></span> </li> <li>三级菜单 <span>></span> </li> </ul> </li> <li>二级菜单 <span>></span> <ul> <li>三级菜单 <span>></span> </li> <li>三级菜单 <span>></span> </li> <li>三级菜单 <span>></span> </li> <li>三级菜单 <span>></span> </li> </ul> </li> <li>二级菜单 <span>></span> <ul> <li>三级菜单 <span>></span> </li> <li>三级菜单 <span>></span> </li> <li>三级菜单 <span>></span> </li> <li>三级菜单 <span>></span> </li> </ul> </li> </ul> </li> <li>一级菜单 <span>></span> </li> </ul> </p> </body> <script type="text/javascript"> let uls = document.querySelectorAll("ul"); //获取所有的ul let lis = document.querySelectorAll("li"); //获取所有的li let liWidth = document.querySelector("#box ul").offsetWidth-2 //li的宽度 -2是为了好看 /* 布局start */ /* * * 通过下面布局中代码实现每个 li.children.length 要么为0 要么为2 * 0 无下级菜单 * 2 有下级菜单 * */ for (let i = uls.length - 1; i >= 0; i--) { if(uls[i].parentNode.nodeName === "LI") { uls[i].parentNode.classList.add("relative"); //相对定位 uls[i].classList.add("absolute"); // 绝对定位 uls[i].style.left = liWidth + "px"; } } for (var i = 0; i < lis.length; i++) { if( lis[i].children.length === 1) { //没有下一级菜单直接删除 lis[i].children[0].outerHTML = ""; }; } /* 布局end */ for (let i = 0; i < lis.length; i++) { // 控制每一个li lis[i].onmouseover = function() { if( lis[i].children.length === 2) { this.children[1].classList.remove("hide"); this.children[1].classList.add("show"); } } lis[i].onmouseout = function() { if( lis[i].children.length === 2) { this.children[1].classList.remove("show"); this.children[1].classList.add("hide"); } } } </script> </html>
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