菜单树代码

var arr = [
    {name:'学习',id: '0',parentId:null},
    {name:'看书',id: '1',parentId:'0'},
    {name:'做题',id: '2',parentId:'0'},
    {name:'苏菲的世界',id: '3',parentId:'1'},
    {name:'高数',id: '4',parentId:'2'},
    {name:'英语',id: '5',parentId:'2'}
    ];
var firstMenu = "<ul>",
len = arr.length;
function tree(arr){
for(let i=0;i<len;i++){
    if(arr[i].parentId == null){
        firstMenu += "<li>"+arr[i].name;
        second(arr, arr[i]);
    }
}
firstMenu += "</li></ul>";
$(".tree").append($(firstMenu));
}
function second(arr, father){
let isFirst = true,
    sec = " ";
for(let i=0;i<len;i++){
    if(arr[i].parentId == father.id){
        if(sec == " "){
            sec = "<ul>"
            firstMenu += sec;
        };
        sec = "<li>"+arr[i].name;
        firstMenu += sec;
        second(arr, arr[i]);
    }
}
if(sec != " ") firstMenu+="</ul></li>";
}
$((){ tree(arr); });
# </script>