reduce ts

const userCollection = [
  {
    name: 'Дмитрий',
    age: 35
  },
  {
    name: 'Сергей',
    age: 30
  }
]

function reduce<T, U>(collection: T[], callback: (result: U, item: T) => U): T
function reduce<T, U>(collection: T[], callback: (result: U, item: T) => U, initItem: U): U
function reduce<T, U>(collection: T[], callback: (result: U, item: T) => U, initItem?: U): U {
  let result: any = initItem !== undefined ? initItem : collection[0];

  let i = initItem !== undefined ? 0 : 1;
  const count = collection.length;
  for(i; i < count; i++) {
    result = callback(result, collection[i]);
  }

  return result;
}

const result = reduce(userCollection, (userResult, current) => {
  userResult[current.name] = current.age;
  return userResult;
});


console.log(result, "sum");