在Node JS中获取Promise错误

Question

Server js:

var user_controller = require('./controllers/user_controller');
passport.use(new passportLocal(function(username, password, done) {
  user_controller.login(username, password).then(function(value) {
    if (value) {
      console.log(value + "true")

      done(null, {
        id: username,
        name: username
      });
    } else {
      console.log(value + "false");
      done(null, null);
    }
  })
}));

USer contoller:

module.exports.login = function(username, password) {
  var status;
  var userid = username;
  User.findOne({
    'username': [userid],
    'password': [password]
  }, function(err, user) {
    if (!user) {
      console.log("logged err");
      status = false;
    } else {
      console.log("login in");
      status = true;
    }
    console.log(status);
    return status;
  });
};

I am doing an async task (db call) in my user_controller.login and it returns a boolean "value"

But when I execute this I am getting error:Cannot read property 'then' of undefined

I saw previous questions on this error but couldnt understand it

Answer 1

I think you can try with callback function. The login function takes one callback param and execute that function at end.

module.exports.login = function(username, password, callback) {
  var status;
  var userid = username;
  User.findOne({
    'username': [userid],
    'password': [password]
  }, function(err, user) {
    if (!user) {
      console.log("logged err");
      status = false;
    } else {
      console.log("login in");
      status = true;
    }
    console.log(status);
    callback(status);
  });
};

While calling the function login pass the third param as a callback function.

var user_controller = require('./controllers/user_controller');
passport.use(new passportLocal(function(username, password, done) {
  user_controller.login(username, password, function(value) {
    if (value) {
      console.log(value + "true")

      done(null, {
        id: username,
        name: username
      });
    } else {
      console.log(value + "false");
      done(null, null);
    }
  })
}));

Note: I am not tested the above code.

Answer 2

You can create promise based functions in Nodejs using Q library.

npm install q

Below code can help you.

module.exports.login=function(username,password){
var status;
var userid=username;

User.findOne({'username':[userid], 'password':[password]},function(err,user){
    var deferred = Q.defer();

    if(err){
       deferred.reject(err); 
    } else{
        deferred.resolve(data);
    }
    return deferred.promise;
});

and use it in Server.js

var user_controller = require('./controllers/user_controller');
passport.use(new passportLocal(function(username, password, done) {
user_controller.login(username, password).then(function(user) {
  done(null, {
    id: username,
    name: username
  });
});