Spotify API，无法链接两个API调用（Authorization-GetSong）

Question

简而言之，我试图实现从API获取令牌的操作，然后获取带有令牌的歌曲。 由于将令牌存储在全局变量中，并且在异步执行getAuthorizationToken之后， getSong会立即调用getSong函数。 因此，对于获取歌曲和获取HTTP 401，使用undefined值调用API。

var XMLHttpRequest = require('xhr2');

function getAuthorizationToken() {
    let request = new XMLHttpRequest();
    request.open('POST', 'https://accounts.spotify.com/api/token/', true);
    request.setRequestHeader("Content-Type", "application/x-www-form-urlencoded");
    request.setRequestHeader('Authorization', "Basic " + Buffer.from(config.clientID + ":" + config.clientSecret).toString('base64'));
    request.onload = function () {
        let data = JSON.parse(this.response);
        if (request.status === 200) {
            console.log(data['access_token']);
            authorizationToken = data['access_token'];
        }
    };
    request.send("grant_type=client_credentials");
}

function getSong() {
    let request = new XMLHttpRequest();
    request.open('GET', 'https://api.spotify.com/v1/tracks/2TpxZ7JUBn3uw46aR7qd6V', true);
    request.setRequestHeader('Authorization', "Bearer " + authorizationToken);
    request.onload = function () {
        let data = JSON.parse(this.response);
        console.log(data)
    };
   request.send();
}
getAuthorizatonToken();
getSong(); //this is invoked before authorizatonToken's value assigned.

我试图用Promise的链接方式。

function getAuthorizationToken() {

return new Promise(() => {
    let request = new XMLHttpRequest();
    request.open('POST', 'https://accounts.spotify.com/api/token/', true);
    request.setRequestHeader("Content-Type", "application/x-www-form-urlencoded");
    request.setRequestHeader('Authorization', "Basic " + Buffer.from(config.clientID + ":" + config.clientSecret).toString('base64'));
    request.onload = function () {
        let data = JSON.parse(this.response);
        if (request.status === 200) {
            console.log(data['access_token']);
            authorizationToken = data['access_token'];
        }
    };
    request.send("grant_type=client_credentials");
    });
}

function getSong() {
    // same method 
}

getAuthorizationToken().then(getSong);

但是，它对于getSong函数不返回任何getSong 。 我对此不确定，但我相信诺言不会等待onload 。

另外，我尝试同步发送第一个请求，但它给出了一个错误；

错误：未执行同步XHR处理

我不熟悉JavaScript编码，我的思维方式出了什么问题？

Answer 1

诺言的问题是您需要解决或拒绝退出诺言并将令牌数据传递给下一个诺言或功能。

一个简单的promise函数如下所示：

var promise = new Promise(function(resolve, reject) {
  setTimeout(function() {
    resolve('foo');
  }, 300);
});

这是最终代码：

var config = require('./config.json');
var XMLHttpRequest = require('xhr2');


function getAuthorizationToken() {
    return new Promise(function (resolve, reject) {
        let request = new XMLHttpRequest();
        request.open('POST', 'https://accounts.spotify.com/api/token/');
        request.setRequestHeader("Content-Type", "application/x-www-form-urlencoded");
        request.setRequestHeader('Authorization', "Basic " + Buffer.from(config.clientID + ":" + config.clientSecret).toString('base64'));

        request.onload = function () {
            if (request.status === 200) {   
                let responseBody = JSON.parse(this.response);                              
                resolve(responseBody["access_token"]);
            }else{
                reject(request.status);
            }
        };
        request.onerror = function () {
            reject(Error("Network Error"));
        };
        request.send("grant_type=client_credentials");
    });

}

function getSong(authorizationToken) {
    return new Promise(function(resolve,reject) {

        let request = new XMLHttpRequest();
        request.open('GET', 'https://api.spotify.com/v1/tracks/2TpxZ7JUBn3uw46aR7qd6V', true);
        request.setRequestHeader('Authorization', "Bearer " + authorizationToken);
        request.onload = function () {
            if (request.status === 200) {   
                let responseBody = JSON.parse(this.response);                              
                resolve(responseBody);
            }else{
                reject(request.status);
            }
        };
        request.onerror = function () {
            reject(Error("Network Error"));
        };
        request.send();
    });
}

getAuthorizationToken().then(function (authorizationToken) {
    getSong(authorizationToken).then(function (data) {
        console.log(data);        
    })
});