js多维数组递归，并且添加层级

var array=[{

        id:"0",
        title:"目录",
        children:[{
            id:"1",
            title:"我的音乐",
            children:[{
                id:"2",
                title:"刘若英",
                children:[{
                    id:"3",
                    title:"后来"
                },{
                    id:"3",
                    title:"我们没有在一起"
                },{
                    id:"3",
                    title:"成全"
                }]
            },{
                id:"2",
                title:"周杰伦"
            },{
                id:"2",
                title:"蔡依林"
            }]
        },{
            title:"我的书籍",
            children:[{
                title:"javascript"
            },{
                title:"html css"
            }]
        }]
    }];
    var items=[];
    function render(arr,level){
        var level=level||0;
        level++;
        var i= 0,len=arr.length;        
        var str="<ul style='padding-left:20px'>"
        for(i=0;i<len;i++){
            str+="<li>"+level+"、"+arr[i].title;
            if(arr[i].children&&arr[i].children.length>0){
                str+=render(arr[i].children,level);
                items.push([{"title":arr[i].title,"id":arr[i].id}]);
            }
            str+="</li>";
        }
        str+="</ul>";
        return str;
    }
    render(array,0);
    document.body.innerHTML=render(array);
    console.log(items);