How could I reduce the length of the code?

The log of the code below is "TypeError: the_hobbit is undefined" why is it so instead of showing the object's length?

• function Book (length, author) {     this.length = length;     this.author = author; } var the_hobbit= Book("J.R.R. Tolkien", 320); console.log(the_hobbit.length);

• Answer:

  It should be var the_hobbit = new Book(320,"J.R.R Tolkien");