Promise all map update array

Found what was wrong, it seems you can't add a property which does not exist in my mongoose model User. To bypass it I did:

let updatedUser = user.toObject();updatedUser.hasCar = !!car;return updatedUser;

Thanks everyone

It seems to work as it is. I made some simple changes to fake out Car.count and removed ObjectId, and it works as expected:

const cars = {1: ['car a', 'car b'], 3: ['car c']};const Car = {  count: (user) => new Promise((resolve, reject) =>                        setTimeout(() => resolve(cars[user.userId]), 1000))};function findCars(users) {  return Promise.all(users.map((user) =>     Car.count({      userId: user._id    })    .then((car) => {      user.hasCar = !!car;      return user;    })  ))  .then(console.log);}const users = [{_id: 1}, {_id: 2}, {_id: 3}];findCars(users);

This returns a Promise, and one second later logs the following to the console:

[{"_id":1,"hasCar":true},{"_id":2,"hasCar":false},{"_id":3,"hasCar":true}]

Note, I originally used the simpler

count: (user) => Promise.resolve(cars[user.userId])

But I wanted to ensure some true async. Neither way had any issues.

You can see this in action on RunKit.