如何使用Async库实现异步操作？

Question

GrabRedisDataByArray = Promise.promisify(function(data, callback) {
    var temp_results = [];

    async.each(data, function(result, done) {

        redis.hgetall('username:' + result, function(err, results) {

            temp_results.push(results);
            done();
        })

    }, function(err) {
        callback(temp_results)
    });

});

Except, it's returning

Unhandled rejection (<[{"server":"9300","user_id":"31","char...>, no stack trace )

--That object data is just some user information stored in the username: key.

---

And my method for data retrieval is:

 GrabRedisDataByArray(data).then(function(data){
         console.log(data)                               
 });

I think my problem is with GrabRedisDataByArray and how it doesn't return anything in the main function scope, but only returns something through its second parameter? If that makes sense? I'm just kind of lost here and trying to understand how I can return that async operation to the main function instead of only returning it through the second parameter callback (Which is I think my promises isn't working correctly)

Edit: This is using the Bluebird library

Answer 1

Well, promisify expects node-style callbacks, so when you're calling callback(temp_results) you are passing an error parameter. It would have to be callback(null, temp_results) .

---

That said, you should not use the async library at all when you're working with promises anyway. Just embrace promises. Or if you insist on using async , at least do it properly:

var grabRedisDataByArray = Promise.promisify(function(data, callback) {
    async.map(data, function(result, done) {
        redis.hgetall('username:' + result, done);
    }, callback);
});

But when promisifying, you should always promisify on the lowest level - in your case redis . Then you don't have to mess around with async callbacks but can simply use Bluebird's Promise.map :

Promise.promisifyAll(redis);
function grabRedisDataByArray(data) {
    return Promise.map(data, function(result) {
        return redis.asyncHgetall('username:' + result);
    });
}