How can I get the value of all the same properties in an object?

Question

So I am doing a npm test on object books . I want to get the value of the title property from the books object. If I call the function getTheTitles(books) , the value of both 'Book' and 'Book2' will be returned. I tried writing my code and run npm test but the result shown that there is one undefined in addition to Book and Book2 . Is there some changes need to be done on my getTheTiles function?The following are the code:

const books = [
    {
      title: 'Book',
      author: 'Name'
    },
    {
      title: 'Book2',
      author: 'Name2'
    }
  ]

---

let titles = ['title'];

  const getTheTitles = function(item) {
    return titles.map(function(k) {
        return item[k];
    })
 }

getTheTitles(books);

------------------ Below are the npm test and it's expected result -----------

const getTheTitles = require('./getTheTitles')

describe('getTheTitles', () => {
    const books = [
      {
        title: 'Book',
        author: 'Name'
      },
      {
        title: 'Book2',
        author: 'Name2'
      }
    ]

  test('gets titles', () => {
    expect(getTheTitles(books)).toEqual(['Book','Book2']);
  });
});

Answer 1

The callback for map function is not quite correct.

You can simply do

 const data = [{ title: 'Book', author: 'Name' }, { title: 'Book2', author: 'Name2' }]; const getTheTitles = (books) => books.map((book) => book.title); console.log(getTheTitles(data));

Answer 2

Yes the function needs some tweaking. Something like this should work:

const getTheTitles = bookList => {
    return bookList.map(book => book.title);
}

That will give you a list of the titles.