marijnh/Eloquent-JavaScript — pull request #33 by lauritzsh (2014-03-24 22:06:23+00:00)
Title: Invoke on instances instead of the class Point

The book does read 'Give the Point prototype two methods', so it would make sense to instantiate Point objects and invoke methods on them instead of the constructor.
This worked for me, so I thought this might save some trouble for others.