蓝鸟递归承诺没有得到 resolved/fulfilled

Question

使用 BlueBird promises，我试图将 getCredentials 变成一个可以像 getCredentials.then(function() { do this and that } ); 一样工作的 promise。不确定我做错了什么，因为当我在 writeToFile 中解决时，promise 不算作 resolved/fullfilled.

function getPassword(user) {
    return new Promise(function(resolve, reject) {
    read({prompt: "Password: ", silent: true, replace: "*" }, function (er, pass) {
        rest.postJson(URL, payload(user, pass))
            .on('fail', httpFail)
            .on('error', conError)
            .on('success', writeToFile);
    });
    });
}

function getCredentials() {
    return new Promise(function(resolve, reject) {
    read({prompt: "Username: "}, function (er, user) {
        getPassword(user);
    });
    });
}

function writeToFile(data, response) {
     return new Promise(function(resolve, reject) {
    tokenFile = 'gulp/util/token-file.json'
    token = {
        id: data.access.token.id,
        expires: data.access.token.expires
    }
    token = JSON.stringify(token);
    fs.writeFile(tokenFile, token, function(err) {
        if (err) throw err;
        console.log("Token was successfully retrieved and written to " .cyan +
            tokenFile .cyan + "." .cyan);
    resolve();
    });
     });
}

module.exports = getCredentials;

Answer 1

getCredentials() 和 getPassword() 没有兑现他们完成时的承诺。他们永远得不到解决。

我从代码中假设您还想将 getPassword 承诺与 writeToFile 承诺链接起来，这样 getPassword 直到 writeToFile 才解析。

可能看起来像这样：

function getPassword(user) {
    return new Promise(function(resolve, reject) {
        read({prompt: "Password: ", silent: true, replace: "*" }, function (er, pass) {
            rest.postJson(URL, payload(user, pass))
                .on('fail', httpFail)
                .on('error', conError)
                .on('success', function(data, response) {
                    writeToFile(data, response).then(resolve);
                });
        });
    });
}

您可能还想实现错误处理。

Answer 2

Not sure what I am doing wrong, because when I resolve in writeToFile the promise is not counted as resolved/fullfilled

好吧，你 return 从 writeToFile 兑现的承诺。
但是从 getPassword 或 getCredentials 中 return 得到的 promise 永远不会是——你没有调用 他们的 resolve 函数。 Promise 构造函数不会神奇地知道其中使用的异步回调，或者将在其中创建承诺。

您不能 return 异步回调中的任何内容，从那里发出结果信号的唯一方法是调用另一个（回调）函数。在 Promise 构造函数的解析器内部，这将是 resolve 和 reject 回调。

您可能希望查看尽可能低的 my rules for promise development. We almost never use the Promise constructor, only to promisify。在你的情况下，那将是

function readAsync(options) {
    return new Promise(function(resolve, reject) {
        read(options, function (err, pass) {
            if (err) reject(err);
            else resolve(pass);
        }
    });
}
function postAsync(url, payload) {
    return new Promise(function(resolve, reject) {
        rest.postJson(url, payload)
        .on('fail', reject)
        .on('error', reject)
        .on('success', resolve);
    });
}

尽管使用 Bluebird 我们可以将第一个简化为

var readAsync = Promise.promisify(read);

和类似用途

var writeFileAsync = Promise.promisify(fs.writeFile, fs);

现在我们有了那些 promise-returning 函数，我们可以应用其余规则并将它们组合在一起，而无需再使用 Promise 构造函数：

function getPassword(user) {
    return readAsync({prompt: "Password: ", silent: true, replace: "*" })
    .then(function(pass) {
        return postAsync(URL, payload(user, pass))
    });
}

function getCredentials() {
    return readAsync({prompt: "Username: "}).then(getPassword);
}

function writeToFile(data, response) {
    var tokenFile = 'gulp/util/token-file.json';
    var token = JSON.stringify({
        id: data.access.token.id,
        expires: data.access.token.expires
    });
    return writeFileAsync(tokenFile, token).then(function() {
        console.log("Token was successfully retrieved and written to " .cyan +
                    tokenFile .cyan + "." .cyan);
    });
}

module.exports = getCredentials;

蓝鸟递归承诺没有得到 resolved/fulfilled

bluebird recursive promise not getting resolved/fulfilled

javascript

node.js

promise

bluebird