why does my function returns undefined?

Question

I'm trying to create a filter to stop duplication in submitting forms, I have used findone and checked if it's null returns true and vise versa, but it always returns undefined

function checkParticipant(fname, mname, lname, foname){
  Participant.findOne({
    fname: fname,
    mname: mname,
    lname: lname,
    foname: foname
  }, function(err,participant){
    if(participant == null){
      return true;
    }else{
      return false;
    }
  });
}

Format your code for better readability – Krishna Prashatt Jun 28 '18 at 11:56 — Krishna Prashatt, Jun 28 '18 at 11:56

score 0 · Answer 1 · answered Jun 28 '18 at 12:04

0

Try using

function checkParticipant(fname, mname, lname, foname){
  Partiipant.findOne({fname:fname, mname:mname, lname:lname, foname:foname }).then( participant => (
   if(participant) return false
   else return true;
))
}

FindOne returns a promise so you`d have to subscribe to it to get the data.

answered Jun 28 '18 at 12:04

Liondj

48
9

As for the if(participant), basically, if the findOne returns a participant, its found and it will return false, vice versa if participant was not found, youll get false – Liondj Jun 28 '18 at 12:05
`return !!participant` ? – thebjorn Jun 28 '18 at 12:17
@thebjorn what? – Liondj Jun 28 '18 at 12:24
Sorry, my eyes crossed a bit.. It should of course be `return !participant;` -- it is a shorter way to write your if/return statement. ( the `return !!participant;` is for when the true branch should return `true`.) – thebjorn Jun 28 '18 at 12:35
Oh, something new, thanks :D – Liondj Jun 29 '18 at 08:40

score 0 · Answer 2 · answered Jun 28 '18 at 12:12

0

Your checkParticipant function does not contain a return statement. Hence it will return undefined.

answered Jun 28 '18 at 12:12

Melvin Vermeer

126
1

score 0 · Answer 3 · answered Jun 28 '18 at 12:13

0

A function returns undefined if a value was not returned.

Please check MDN before posting.

answered Jun 28 '18 at 12:13

leonardofed

936
2
9
24

itsundefined · Answer 4 · 2018-06-28T12:43:16.100

0

The problem is that you are trying to return from an asynchronous function. This is not possible. Check this answer on how to solve it

edited Jun 28 '18 at 12:43

answered Jun 28 '18 at 12:35

itsundefined

1,409
2
12
32

score 0 · Answer 5 · answered Jun 28 '18 at 12:47

Nothing wrong with code you have returned. Its just about concept of Javascript callback function.

function timeOut()
{ 
  setTimeout(function(){ return true; })
};

timeOut(); // returns undefined

Executing this function returns undefined becuase, the query has callback function which runs in different context and returns nothing that means undefined.

So to solve your problem, you need to update the code as follows if your ORM supports the promises.

function checkParticipant(fname, mname, lname, foname){
   return Partiipant.findOne({fname:fname, mname:mname, lname:lname, foname:foname 
}).then( participant => (
   if(participant == null)
   {
       return true;
   }
   else return false;
  ))
}

Hope this will solve your problem.

why does my function returns undefined?

5 Answers5