It's a small point to make but when one clicks on the Save and Submit button for this exercise after entering what seems to be the expected input the console response reads "J.K. Rowling". Perhaps the intended response was to read "J.R.R. Tolkien".
Thanks very much for hosting these lessons.
// Use our new constructor to make the_hobbit in one line var the_hobbit = new Book(320, "J.R.R. Tolkien");