回调地狱

回调地狱：多层回调函数嵌套

例子：网易云音乐

<script src="https://cdn.bootcss.com/jquery/3.4.1/jquery.js"></script>

 var baseUrl="https://music.aityp.com/";
        $.ajax({
            url:baseUrl+"top/playlist",
            type:"get",
            data:{
                cat:"华语"
            },
            dataType:"json",
            success:res=>{
                var {playlists}=res;
                var item=playlists[0];
                console.log(item)
                $.ajax({
                    url:`${baseUrl}playlist/detail?id=${item.id}`,
                    type:"get",
                    success:res=>{
                        let id=res.playlist.trackIds[0].id;
                        console.log(id)
                        $.ajax({
                            url:`${baseUrl}song/url?id=${id}`,
                            success:res=>{
                                console.log(res)
                            }
                        })
                    }
                })
            }
        })

解决回调地狱的方法

1.Promise()