Reduce key value pairs in a javascript object based on a given array

Use reduce on userFields and build

const user = {
  email: "[email protected]",
  name: "Bob",
  surname: "Smith",
};

const userFields = [`email`, `name`];

const newUser = userFields.reduce(
  (acc, key) => Object.assign(acc, { [key]: user[key] }),
  {}
);
console.log(newUser)

For me, the simplest thing to do would be to loop through the passlist and build an object:

const result = {};
for (const name of userFields) {
    result[name] = user[name];
}

Live Example:

const user = {
   "email": "[email protected]",
   "name": "Bob",
   "surname": "Smith",
};

const userFields = [`email`, `name`];

const result = {};
for (const name of userFields) {
    result[name] = user[name];
}

console.log(result);

You could use map and Object.fromEntries, but I don't think it buys you anything:

const result = Object.fromEntries(
    userFields.map(name => [name, user[name]])
);

Live Example:

const user = {
   "email": "[email protected]",
   "name": "Bob",
   "surname": "Smith",
};

const userFields = [`email`, `name`];

const result = Object.fromEntries(
    userFields.map(name => [name, user[name]])
);

console.log(result);

FWIW, for me reduce is the wrong tool for this (or indeed, almost anything else outside of Functional Programmning with predefined, reusable reducer functions), not least because the accumulator in a reduce solution would never change (it's always the same object). reduce where a simple loop suffices is just overcomplicated and easy to get wrong. (An opinion which isn't solely mine, btw.)

You could use Object.fromEntries() method. Traverse the userFields array using Array.prototype.map() and make a list of key-value pair array. At last, from that list transform it into the required object by using Object.entries() method.

const user = {
  email: '[email protected]',
  name: 'Bob',
  surname: 'Smith',
};

const userFields = [`email`, `name`];
const ret = Object.fromEntries(userFields.map((x) => [x, user[x]]));
console.log(ret);