Ndtyjky

In this case, method 3 works first and i am getting error. Its priority has to be like method 1, method 2, and method 3. Are these methods promises ? And promises work as asynchronous.

I want check if new user's username and email in use or not. If username or email are not in use, then register it.

How to i solve this problem ? I'm new at nodejs.

module.exports.addUser = function(newUser, callback) {



    // method 1

    User.countDocuments({username: newUser.username}).then(count => {

        if(count > 0) {

            console.log("username in use");

            callback("username in use", null);

            return;

        }});



    // method 2

    User.countDocuments({email: newUser.email}).then(count => {

        if(count > 0) {

            console.log("email in use");

            callback("email in use", null);

            return;

        }});



    // method 3 , this method works first

    bcrypt.genSalt(10, (err, salt) => {

        console.log("salt here");

        bcrypt.hash(newUser.password, salt, (err, hash) => {

            if(err) throw err;

            newUser.password = hash;

            newUser.save(callback);

        });

    });

};

Output:

salt here

username in use

email in use



(node:7972) UnhandledPromiseRejectionWarning: Error: Can't set headers after they are sent.

    at validateHeader (_http_outgoing.js:491:11)

    at ServerResponse.setHeader (_http_outgoing.js:498:3)

    at ServerResponse.header (C:UserscycloneDesktopmy_authnode_modulesexpresslibresponse.js:767:10)

    at ServerResponse.send (C:UserscycloneDesktopmy_authnode_modulesexpresslibresponse.js:170:12)

    at ServerResponse.json (C:UserscycloneDesktopmy_authnode_modulesexpresslibresponse.js:267:15)

    at User.addUser (C:UserscycloneDesktopmy_authroutesusers.js:20:17)

    at User.countDocuments.then.count (C:UserscycloneDesktopmy_authmodelsuser.js:48:13)

    at <anonymous>

    at process._tickCallback (internal/process/next_tick.js:189:7)

(node:7972) UnhandledPromiseRejectionWarning: Unhandled promise rejection. This error originated either by throwing inside of an async function without a catch block, or by rejecting a promise which was not handled with .catch(). (rejection id: 1)

(node:7972) [DEP0018] DeprecationWarning: Unhandled promise rejections are deprecated. In the future, promise rejections that are not handled

will terminate the Node.js process with a non-zero exit code.

events.js:183

      throw er; // Unhandled 'error' event

      ^



Error: Can't set headers after they are sent.

    at validateHeader (_http_outgoing.js:491:11)

    at ServerResponse.setHeader (_http_outgoing.js:498:3)

    at ServerResponse.header (C:UserscycloneDesktopmy_authnode_modulesexpresslibresponse.js:767:10)

    at ServerResponse.send (C:UserscycloneDesktopmy_authnode_modulesexpresslibresponse.js:170:12)

    at ServerResponse.json (C:UserscycloneDesktopmy_authnode_modulesexpresslibresponse.js:267:15)

    at User.addUser (C:UserscycloneDesktopmy_authroutesusers.js:22:17)

    at C:UserscycloneDesktopmy_authnode_modulesmongooselibmodel.js:4518:16

    at model.$__save.error (C:UserscycloneDesktopmy_authnode_modulesmongooselibmodel.js:422:7)

    at C:UserscycloneDesktopmy_authnode_moduleskareemindex.js:315:21

    at next (C:UserscycloneDesktopmy_authnode_moduleskareemindex.js:209:27)

    at C:UserscycloneDesktopmy_authnode_moduleskareemindex.js:182:9

    at process.nextTick (C:UserscycloneDesktopmy_authnode_moduleskareemindex.js:499:38)

    at _combinedTickCallback (internal/process/next_tick.js:132:7)

    at process._tickCallback (internal/process/next_tick.js:181:9)

[nodemon] app crashed - waiting for file changes before starting...

The single fact that "then" is used after countDocuments does indicate that it's a promise and thus asynchronous.

The easiest solution at this point, would be to define your addUser function as async.

module.exports.addUser = async function(newUser, callback) {



  // method 1

  const count1 = await User.countDocuments({

    username: newUser.username

  });



  if (count1 > 0) {

    console.log("username in use");

    callback("username in use", null);

    return;

  };



  // method 2

  const count2 = await User.countDocuments({

    email: newUser.email

  });



  if (count2 > 0) {

    console.log("email in use");

    callback("email in use", null);

    return;

  };



  // method 3 , this method works first

  bcrypt.genSalt(10, (err, salt) => {

    console.log("salt here");

    bcrypt.hash(newUser.password, salt, (err, hash) => {

      if (err) throw err;

      newUser.password = hash;

      newUser.save(callback);

    });

  });

};

However, now it's quite pointless to have a callback function for addUser since an async function automatically returns a promise. I'd recommend doing something like so...

module.exports.addUser = async function(newUser) {



  // method 1

  const count1 = await User.countDocuments({

    username: newUser.username

  });



  if (count1 > 0) {

    throw Error("username is in use");

  };



  // method 2

  const count2 = await User.countDocuments({

    email: newUser.email

  });



  if (count2 > 0) {

    throw Error("email in use");

  };



  let result = null;

  // method 3 , this method works first

  bcrypt.genSalt(10, (err, salt) => {

    console.log("salt here");

    bcrypt.hash(newUser.password, salt, (err, hash) => {

      if (err) throw err;

      newUser.password = hash;

      result = await newUser.save(callback);

    });

  });



  return result;



};

and in use it would look like:

addUser(someUserObject).then(result=>console.log(result)).catch(error=>{

  //Example: username in use

  console.log(error.message)

});