If we have a book object but we do not give it a "subtitle" property, will following code return undefined?

Question

If we have a book object but we do not give it a "subtitle" property, will following code return undefined?
bar len = book.subtitle.length;

Answer 1

Why subtitle, can you give other property?

Answer 2

it doesn't meter. You can give it any name, just wondering does it returns "undefined"

Answer 3

@Jamie what value have a property that doesn't exist?

Answer 4

@Jamie If we theoretically have an object and this object doesn't have a "subtitle" property, will "bar len = book.subtitle" return undefined?