Step 4

step4.js

const users = [
  { firstName: 'Jane', lastName: 'Foo' },
  { firstName: 'John', lastName: 'Bar' },
  { firstName: 'Jill', lastName: 'Err' }
]

function findMatchingAndMoveToFirst (users, shouldBeFirst) {
  return users.reduce((accumulator, current) => {
    return current.firstName === shouldBeFirst.firstName &&
      current.lastName === shouldBeFirst.lastName
      ? [current, ...accumulator]
      : [...accumulator, current]
  }, [])
}

const reArrangedUsers = findMatchingAndMoveToFirst(users, {
  firstName: 'John',
  lastName: 'Bar'
})
console.log(reArrangedUsers)