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.

You want to check whether .some elements in books are an instanceof Book… — deceze
– deceze ♦, Commented Jul 18, 2017 at 11:55
wow.. -2 already just because I didn't know about .some and instanceof. It worked @deceze thanks! — Luca S.
– Luca S., Commented Jul 18, 2017 at 12:00

Alberto Trindade Tavares · Accepted Answer · 2017-07-18 11:56:22Z

6

You literally have instanceof:

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

answered Jul 18, 2017 at 11:56

Alberto Trindade Tavares

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