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
}

• Phil: Is this something you need to do often? Are the three specific titles dynamic or fixed? Is it always three?
• brandonstiles: This function could get 5k hits/mo, so it'd be fairly high traffic. The 3 titles ARE specific though - I'd always be looking for the same 3 in a possible array of 1-5 books.

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"));

• brandonstiles: Nice call out! In this case, it'd only be dynamic on a request-by-request basis. So a client could send in 1-5 books, and I'm checking to make sure 3 specific ones exist on that request before I do some work.

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 );