How can I return new data in map function?

Question

I have a jsonData (objects in array), and I am using map function to get completely new data.
So basically, eachData becomes newEachData.
My code looks like this:

let jsonData = data.toJSON();
let newData = jsonData.map((**eachData**) => {
   User.query({
      where: {userid: eachData.userid_b},
      select: ['username', 'userid']
   }).fetch().then(userData => {
      let **newEachData** = userData.toJSON();
   })
})
console.log(newData);

How to return new value?

Just to be clear, I am retrieving new data from database using eachData right after map function.