使用 BlueBird promise ,我尝试将 getCredentials
变成一个将作为 getCredentials.then(function() { do this and that } );
工作的 promise 。不确定我做错了什么,因为当我在 writeToFile
中解析时, promise 不被视为已解决/已完成。
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;
最佳答案
Not sure what I am doing wrong, because when I resolve in writeToFile the promise is not counted as resolved/fullfilled
好吧,您从 writeToFile
返回的 promise 已实现。
但是从 getPassword
或 getCredentials
返回的 promise 永远不会 - 您没有调用它们 resolve
函数。 Promise 构造函数不会神奇地知道其中使用的异步回调,或者其中会创建 Promise。
您无法从异步回调中返回
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。
您可能想看看my rules for promise development 。我们几乎从不使用 Promise
构造函数,只是为了 promisify在尽可能低的水平。在你的情况下,那就是
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);
});
}
虽然使用 Bluebird 我们可以简化第一个
var readAsync = Promise.promisify(read);
和类似用途
var writeFileAsync = Promise.promisify(fs.writeFile, fs);
现在我们有了这些 Promise 返回函数,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;
关于javascript - Bluebird 递归 promise 未得到解决/履行,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/28958458/