How to check if array contains instance of an object in Javascript?

Question

I have an object like this:

MyLibrary {
 books: 
 [ Book {
 bookType: 'romance'
 } 
 ]
}

Book is a class.

I would like to write a test to check if books contain an object that is an instance of Book. I was expecting to use something like MyLibrary.books.indexOf('Book') but it returns -1 even when Book exist.

• deceze: You want to check whether .some elements in books are an instanceof Book...
• Luca S.: wow.. -2 already just because I didn't know about .some and instanceof. It worked @deceze thanks!

Answer 1

You literally have instanceof:

var hasBook = books.some((book) => book instanceof Book);