使用Promise.all（）进行多个http / oauth查询

Question

I'm trying to wait for the output of two OAuth calls to an API, and I'm having trouble retrieving the data from those calls. If I use Promise.all(call1,call2).then() I am getting information about the request object.

First, here's the setup for the fitbit_oauth object:

var fitbit_oauth = new OAuth.OAuth(
    'https://api.fitbit.com/oauth/request_token',
    'https://api.fitbit.com/oauth/access_token',
    config.fitbitClientKey,
    config.fitbitClientSecret,
    '1.0',
    null,
    'HMAC-SHA1'
);

foodpath = 'https://api.fitbit.com/1/user/-/foods/log/date/' + moment().utc().add('ms', user.timezoneOffset).format('YYYY-MM-DD') + '.json';
activitypath = 'https://api.fitbit.com/1/user/-/activities/date/' + moment().utc().add('ms', user.timezoneOffset).format('YYYY-MM-DD') + '.json';

Promise.all([fitbit_oauth.get(foodpath, user.accessToken, user.accessSecret), 
             fitbit_oauth.get(activitypath, user.accessToken,   
                                            user.accessSecret)])
                .then(function(arrayOfResults) {
                    console.log(arrayOfResults);
                }

I want arrayOfResults to give me the data from the calls, not information about the requests. What am I doing wrong here? I'm new to promises so I'm sure this is easy for someone who isn't.

The callback for a single fitbit_oauth call is as follows:

fitbit_oauth.get(
                'https://api.fitbit.com/1/user/-/activities/date/' + moment().utc().add('ms', user.timezoneOffset).format('YYYY-MM-DD') + '.json',
                user.accessToken,
                user.accessSecret,
                function (err, data, res) {
                    if (err) {
                        console.error("Error fetching activity data. ", err);
                        callback(err);
                        return;
                    }

                data = JSON.parse(data);
                console.log("Fitbit Get Activities", data);

                // Update (and return) the user
                User.findOneAndUpdate(
                    {
                        encodedId: user.encodedId
                    },
                    {
                        stepsToday: data.summary.steps,
                        stepsGoal: data.goals.steps
                    },
                    null,
                    function(err, user) {
                        if (err) {
                            console.error("Error updating user activity.", err);
                        }
                        callback(err, user);
                    }
                );
            }
        );

Thanks to jfriend00 I got this working, here's the new code:

function fitbit_oauth_getP(path, accessToken, accessSecret) {
    return new Promise (function(resolve, reject) {
        fitbit_oauth.get(path, accessToken, accessSecret, function(err, data, res) {
            if (err) {
                 reject(err);
            } else {
                 resolve(data);
            }
        }
     )
})};

Promise.all([fitbit_oauth_getP(foodpath, user.accessToken, user.accessSecret), 
    fitbit_oauth_getP(activitypath, user.accessToken, user.accessSecret)])
        .then(function(arrayOfResults) {
            console.log(arrayOfResults);
    });

Answer 1

Promise.all() only works properly with asynchronous functions when those functions return a promise and when the result of that async operation becomes the resolved (or rejected) value of the promise.

There is no magic in Promise.all() that could somehow know when the fitbit functions are done if they don't return a promise.

You can still use Promise.all() , but you need to "promisify" the fitbit functions which is a small wrapper around them that turns their normal callback approach into returning a promise that was then resolved or rejected based on the callback result.

Some references on creating a promisified wrapper:

Wrapping Callback Funtions

How to promisify?

---

If you have an async function that accepts a callback to provide the async result such as fs.rename(oldPath, newPath, callback) , then you can "promisify" it like this:

function renameP(oldPath, newPath) {
    return new Promise(function(resolve, reject) {
        fs.rename(oldPath, newPath, function(err) {
            if (err) {
                reject(err);
            } else {
                resolve();
            }
        });
    });
};


renameP("orig.txt", "backup.txt").then(function() {
   // successful here
}, function(err) {
    // error here
});

---

Some promise libraries such as Bluebird have a built in .promisify() method that will do this for you (it will return a function stub that can be called on any function that follows the node.js async calling convention).