Javascript - check if certain values are in an array of objects

Question

Say I have an array of 5 objects, each with 2 keys (eg, 'title' & 'author').

I want to check the truthiness that 3 SPECIFIC titles exist in the array.

What's the best way to do that?

I have the following... but it doesn't seem very efficient:

const books = [
  { title: 'Book1', author: 'Author1' },
  { title: 'Book2', author: 'Author2' },
  { title: 'Book3', author: 'Author3' },
  { title: 'Book4', author: 'Author4' },
  { title: 'Book5', author: 'Author5' },
];

const certainBooks = books.some((b) => b.title === 'Book2')
   && books.some((b) => b.title === 'Book3')
   && books.some((b) => b.title === 'Book5')

if (certainBooks) {
  // Do stuff
}

Answer 1

If the values and number of titles is dynamic, it might be worth creating an index of titles in the array; something with O(1) time complexity for faster lookups

const books = [
  { title: 'Book1', author: 'Author1' },
  { title: 'Book2', author: 'Author2' },
  { title: 'Book3', author: 'Author3' },
  { title: 'Book4', author: 'Author4' },
  { title: 'Book5', author: 'Author5' },
];

const titleIndex = new Set(books.map(({ title }) => title));

const titlesExist = (...titles) =>
  titles.every(title => titleIndex.has(title))

console.log("Book2, Book3, Book5:", titlesExist("Book2", "Book3", "Book5"));
console.log("Book1:", titlesExist("Book1"));
console.log("Book5, Book6:", titlesExist("Book5", "Book6"));

Answer 2

A more general approach would be to map the books to their titles, then check that .every one of the titles you're looking for exists.

const books = [
  { title: 'Book1', author: 'Author1' },
  { title: 'Book2', author: 'Author2' },
  { title: 'Book3', author: 'Author3' },
  { title: 'Book4', author: 'Author4' },
  { title: 'Book5', author: 'Author5' },
];
const titles = books.map(({ title }) => title);
const toFind = ['Book2', 'Book3', 'Book5'];
if (toFind.every(title => titles.includes(title))) {
  console.log('do stuff');
}

If the array of books is large, you could benefit by making titles a Set instead of an array - Set#has is faster than Array#includes when there are a lot of elements.

Answer 3

You could loop over them

const books = [
  { title: "Book1", author: "Author1" },
  { title: "Book2", author: "Author2" },
  { title: "Book3", author: "Author3" },
  { title: "Book4", author: "Author4" },
  { title: "Book5", author: "Author5" },
];

const booksNeeded = ["Book2", "Book3", "Book4"];
for (let book of books) {
  const lookForIndex = booksNeeded.findIndex(
    (title) => title.toLowerCase() === book.title.toLowerCase()
  );
  if (lookForIndex !== -1) {
    booksNeeded.splice(lookForIndex, 1);
  }
  if (!booksNeeded.length) {
    break; // Early break if all the books has been found
  }
}


if (!booksNeeded.length) {
  console.log("Do Something");
} else {
  console.log("Something else");
}

Answer 4

const books = [
  { title: 'Book1', author: 'Author1' },
  { title: 'Book2', author: 'Author2' },
  { title: 'Book3', author: 'Author3' },
  { title: 'Book4', author: 'Author4' },
  { title: 'Book5', author: 'Author5' },
];

let ops     = 0;
let search  = [ "Book2", "Book3", "Book4" ];
let { length } = search;

for ( let i = 0, len = books.length; length && i < len; i++ ){
  ops++;
  if ( search.includes(books[i].title) ){
    length--;
  }
}

if ( !length ){
  console.log("All books found!");
} else {
  console.log("Not all books found!")
}
console.log( "Number of operations: ", ops );