tp-02-start.js

const data = {
  persons: [
    { id: 0, name: "Sherlock Holmes", numbers: ["555-0101", "555-0199"] },
    { id: 1, name: "John Watson", numbers: ["555-0102", "555-0198"] }
  ],
  groups: [
    { id: 0, name: "Londonians", personsIds: [0, 1] },
    { id: 1, name: "Doctors", personsIds: [1] }
  ]
}

const lastPersonId = 1
const lastGroupId = 1

function getPerson(personId) {
  return data.persons.find(p => p.id === personId)
}
// 
function createPerson(personData) {
  const newPerson = Object.assign({ id: lastPersonId + 1 }, personData)
  lastPersonId++
  data.persons.push(newPerson)
  return newPerson
}

module.exports.getPerson = getPerson
module.exports.createPerson = createPerson