Using callback function inside array.map javascript

Question

I am trying to bcrypt password for every user in an array.

router.post("/insertuser", (req, res) => {

  var promises = users.map((item) => {

    bcrypt.genSalt(10)
      .then((salt) => {
        return item
      })    
  })

  Promise.all(promises)
    .then((results) => {
      console.log(results)
      res.json({
        "data": results
      })
    })    
})//end route

But I am getting results = [undefined,undefined].

How can I return array element from bcrypt.genSalt(10).then

Please help as I am new to ES6

EDIT: My user users array is like this:

[{ "username": "admin", "admin": true} ]

your map callback doesn't return anything, therefore, promises will be an array of undefined - you need to return something in (item) => { /* here */} — Jaromanda X
– Jaromanda X, Commented Nov 3, 2017 at 5:32
... perhaps return bcrypt.genSalt(10) - that way you're returning something — Jaromanda X
– Jaromanda X, Commented Nov 3, 2017 at 5:33
Or just don’t use a block. Just use ….map(item => bcrypt.genSalt(10).then(salt => item)). — Sebastian Simon
– Sebastian Simon, Commented Nov 3, 2017 at 5:37

Shailendra Pal · Accepted Answer · 2017-11-03 05:58:42Z

1

Simply return the promise from bcrypt.genSalt.

router.post("/insertuser", (req, res) => {

  var promises = users.map((item) => {

    return bcrypt.genSalt(10)
      .then((salt) => {
        return item
      })    
  })

  Promise.all(promises)
    .then((results) => {
      console.log(results)
      res.json({
        "data": results
      })
    })    
})//end route

edited Nov 3, 2017 at 5:58

answered Nov 3, 2017 at 5:37

Shailendra Pal

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2 Comments

Jaromanda X Over a year ago

Simply return the bcrypt.genSalt's result. - it's actually going to return the Promise, not the result, and the resolved value will be item

raju Over a year ago

Thanks a lot sir. You saved my day.

Amit Singh · Accepted Answer · 2017-11-03 06:03:34Z

When you add .then() after any promise it will directly get resolved. In your code users.map() will run synchronously and the promises will have undefined. Here is the code you can use :

router.post("/insertuser", (req, res) => {
    var promises = users.map((item) => {
      return bcrypt.genSalt(10);
    })

    Promise.all(promises)
      .then((results) => {
        console.log(results)
    });  
})//

Also notice that salt is used to generate hash. You are only generating salt. To generate hash of password also add bcrypt.hash(password,salt). Here is the code :

var promises = users.map((item) => {
  return bcrypt.genSalt(10);
})

Promise.all(promises)
  .then((results) => {
    promises = results.map((item, index) => {
      return bcrypt.hash(users[index], item);
    });
    return Promise.all(promises);
  })
  .then(result => {
    console.log(result);
  })
  .catch(err => {
    console.log(err);
  });

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