Typescript const Array to object

Question

const persons = [
  {
    name: "John",
    age: 80,
  },
  {
    name: "Julia",
    age: 78,
  },
] as const;

function makePersonsByName(people: typeof persons): {
  [key in typeof persons[number]["name"]]: typeof persons[number];
} {
  let object = {};

  for (let person of persons) {
    object = object
      ? {
          ...object,
          [person.name]: person,
        }
      : {
          [person.name]: person,
        };
  }
  return object;
}

the above code is giving me this error

Type '{}' is missing the following properties from type '{ John: { readonly name: "John"; readonly age: 80; } | { readonly name: "Julia"; readonly age: 78; }; Julia: { readonly name: "John"; readonly age: 80; } | { readonly name: "Julia"; readonly age: 78; }; }': John, Julia

what is the best way to fix this

Dean · Accepted Answer · 2022-07-14 18:00:48Z

2

const persons = [
    {
        name: "John",
        age: 80,
    },
    {
        name: "Julia",
        age: 78,
    },
] as const;

type PersonName = typeof persons[number]["name"];
type Person = typeof persons[number];
// optional to allow empty object to be assignable to this type
type NewlyMappedPerson = {
    [key in PersonName]?: Person;
};

function makePersonsByName(people: typeof persons): NewlyMappedPerson {
    let object: NewlyMappedPerson = {};
    // use reduce to iterate over array and add to the object
    return persons.reduce((acc, person) => {
        return { ...acc, [person.name]: person };
    }, object);
}

console.log(makePersonsByName(persons));

answered Jul 14, 2022 at 18:00

Dean

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