问题:

Hiyas. I have a simple app whereby a client is expecting a promise as a result, but upon calling the resolve() method, the promise keeps returning undefined as the result.

The client code:

UsersRepo.findOneAsync({id: id}).then(function(err, result) {     console.log("UserService promise resolution", err, result); });

This outputs "null" and "undefined", for err and result, respectively

The code that is doing the work and returning the promise:

findOneAsync: function(args) {     var where = ""; //omitted      var promise = new Promise(function(resolve, reject) {         db.query("Select * from users" + where + " limit 1", function(err, result) {             var res = { id: 1, username: 'username', firstName: 'First', lastName: 'Last' };              if(err != null) {                 console.log("REJECT", err);                 reject(err);             }             else {                 console.log("RESOLVE", res);                 resolve(null, res);             }         });     });      return promise; }

As you can see, I'm just returning some static data for this test (the 'res' variable). In the client code, the console statement always prints out:

UserService promise resolution null undefined

I don't get this. It looks like I'm doing everything correctly: calling the resolve() method with the data, and the client code is using .then(function(err, result)) properly, so it seems. Why isn't data being received from the client end?

Thanks for any help!

==>

Solution:

As mentioned below, Bluebird's reject and resolve only take one argument. The first 'null' was only being seen. Changing the code to 'resolve(res)' worked. Thanks guys.

回答1:

Resolve/Reject both accept a single parameter ... hence why your result is undefined, as the second value you pass to resolve is never used, and the first is null

What you want to do instead is

UsersRepo.findOneAsync({id: id}).then(function(result) {     console.log("UserService promise resolution", result); }).catch(function(err) {     console.log("UserService promise error", err); });  findOneAsync: function(args) {     var where = ""; //omitted      var promise = new Promise(function(resolve, reject) {         db.query("Select * from users" + where + " limit 1", function(err, result) {             var res = { id: 1, username: 'username', firstName: 'First', lastName: 'Last' };              if(err != null) {                 console.log("REJECT", err);                 reject(err);             }             else {                 console.log("RESOLVE", res);                 resolve(res);             }         });     });      return promise; }

回答2:

Bluebird's then does not take in an err. Instead, then takes in two functions, the first being for resolve, and the second for being reject. you can also use catch for handling errors.

http://bluebirdjs.com/docs/api/then.html

Edit: @JaromandaX is correct, the resolve function should only take in one parameter.

You should only resolve(res), in addition to not expecting the error object to get passed into the then callback.

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