6-1 promise

1.promise 将函数的状态暂停/凝固

解决回调地狱

    <script>
        /* 我们使用promise的时候会将函数的状态暂停/凝固 
        new Promise
        1.使用new 关键字实现promise
        2.promise有两种状态resolve,reject
        3.promise函数不会马上触发，要通过一个then函数去触发
        4.then触发的是resolve(成功)的状态，catch触发失败的状态
        resolve -->成功
        reject  -->失败
        */
        function go(){
            return new Promise((resolve,reject)=>{
                resolve(1);
                reject(2)
            })
        }
        // go().then(res=>{
        //     console.log(res)
        // }).catch(err=>{
        //     console.log(err)
        //  })
    </script>

2.封装promise

    <script>
        function http(){
            return new Promise((resolve,reject)=>{
                $.ajax({
                    url:"https://music.aityp.com/top/playlist/cat=华语",
                    type:"get",
                    success:res=>{
                        resolve(res)
                    },
                    error:err=>{
                        reject(err)
                    }
                })
            })
        }
        http().then(res=>{
            console.log(res)
        })
    </script>

3.网易云

//http-promise.js
var baseUrl="https://music.aityp.com/"
function http(url){
    return new Promise((resolve,reject)=>{
        $.ajax({
            url:baseUrl+url,
            type:"get",
            dataType:"json",
            success:res=>{
                resolve(res)
            },
            error:err=>{
                reject(err)
            }
        })
    })
}

//promise.html
    <script>
        http("top/playlist?cat=华语").then(res=>{
            let id=res.playlists[0].id;
            return id
        }).then(res=>{
            http(`playlist/detail?id=${res}`).then(res=>{
                let id=res.playlist.trackIds[0].id;
                return id
            }).then(res=>{
                http(`song/url?id=${res}`).then(res=>{
                    console.log(res)
                })
            })
        })
    </script>