Return a number for the amount of times an object value appears as another object value

Question

Example of account object in the accounts array:

const accounts = [
  {
    id: "5f446f2ecfaf0310387c9603",
    picture: "https://api.adorable.io/avatars/75/esther.tucker@zillacon.me",
    age: 25,
    name: {
      first: "Esther",
      last: "Tucker",
    },
    company: "ZILLACON",
    email: "esther.tucker@zillacon.me",
    registered: "Thursday, May 28, 2015 2:51 PM",
  },

Example of a book object in the books array:

const books = [
  {
    id: "5f447132d487bd81da01e25e",
    title: "sit eiusmod occaecat eu magna",
    genre: "Science",
    authorId: 8,
    borrows: [
      {
        id: "5f446f2e2cfa3e1d234679b9",
        returned: false,
      },
      {
        id: "5f446f2ed3609b719568a415",
        returned: true,
      },
      {
        id: "5f446f2e1c71888e2233621e",
        returned: true,
      },
      {
        id: "5f446f2e6059326d9feb9a68",
        returned: true,
      },
      {
        id: "5f446f2ede05a0b1e3394d8b",
        returned: true,
      },
      {
        id: "5f446f2e4081699cdc6a2735",
        returned: true,
      },
      {
        id: "5f446f2e3900dfec59489477",
        returned: true,
      },
      {
        id: "5f446f2e6059326d9feb9a68",
        returned: true,
      },
      {
        id: "5f446f2e409f8883af2955dd",
        returned: true,
      },
      {
        id: "5f446f2e3900dfec59489477",
        returned: true,
      },
      {
        id: "5f446f2eae901a82e0259947",
        returned: true,
      },
      {
        id: "5f446f2ef2ab5f5a9f60c4f2",
        returned: true,
      },
      {
        id: "5f446f2ea6b68cf6f85f6e28",
        returned: true,
      },
      {
        id: "5f446f2eed18105706d6ca19",
        returned: true,
      },
      {
        id: "5f446f2eae901a82e0259947",
        returned: true,
      },
      {
        id: "5f446f2e91c2af00cb74e82b",
        returned: true,
      },
      {
        id: "5f446f2e5aa2bb5545a0f8a6",
        returned: true,
      },
      {
        id: "5f446f2ea508b6a99c3e42c6",
        returned: true,
      },
      {
        id: "5f446f2e50cc2da9cd80efdb",
        returned: true,
      },
      {
        id: "5f446f2e0b3e2ff72fc503e7",
        returned: true,
      },
      {
        id: "5f446f2e91c2af00cb74e82b",
        returned: true,
      },
      {
        id: "5f446f2ef795e593cd3cd19d",
        returned: true,
      },
      {
        id: "5f446f2e2f35653fa80bf490",
        returned: true,
      },
      {
        id: "5f446f2e7b9cd304fed3a8bc",
        returned: true,
      },
      {
        id: "5f446f2ed9aac23c0340aab2",
        returned: true,
      },
    ],
  },

I need my function to return a number that represents the number of times the account's ID appears in any book's borrow array.

Here's what I have:

function getTotalNumberOfBorrows(account, books) {
  const accId = account.id;
  let idBorrowed = books.filter((book) => accId === book.borrows.id);
  return idBorrowed.length;
}

I'm getting 0 when I should get 2 in the test. Please note that I've just finished learning advanced functions and am expected to use find, filter, map, reduce, and destructuring objects when needed. Thanks for any help/advice.

Answer 1

Another possible approach if you need to use "advanced" functions

function getTotalNumberOfBorrows(account, books) {
  const { id: accId } = account;

  return books.reduce((accumulator, book) => {
    return (
      accumulator +
      book.borrows
        .filter(borrow => borrow.id === accId)
        .reduce((accumulatorBorrows, borrow) => accumulatorBorrows + 1, 0)
    );
  }, 0);
}

Working Stackblitz

Answer 2

borrows is an array, you need to iterate over it to get to the id properties of each borrowing.

function getTotalNumberOfBorrows(account, books) {
  const accId = account.id;
  let total = 0;
  books.forEach(book => book.borrows.forEach(borrow => accId === borrow.id && total++));
  return total;
}