CODEWITHSUNDEEP
javascriptmongoosepromisebluebird
MBehtemam
MBehtemam

Reputation: 7919

Why when promise calling another promise return 'undefined'

in my application i work with mongoose and mongodb , in one scenario i need to calling promise from another promise, but promise return undefined, my code is 

function first (num) {
  return new Promise(function(resolve,reject){
    if(num % 2 === 0){
      resolve(num);
    }
    else{
      reject('Error Happend');
    }
  })
}


function second(num){
 first(num).then(function(res){
   return res;
 }).catch(function(err){
   return err;
 })
}

console.log(second(2))
<script src="https://cdn.jsdelivr.net/bluebird/latest/bluebird.js"></script>

in this case i pass 2 to second function and i want it return 2 but it return undefined, i search on SF and find some topic about this but nothing of them solve my problem.

Upvotes: 0

Views: 75

Answers (1)

Quentin
Quentin

Reputation: 943207

You are logging the return value of second(2), but the second function has no return statement in it, so it will always return undefined.

Note that the function expressions you pass to then and catch (which do have return statements are not the second function itself).

Upvotes: 2

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