Uncaught Type Error

I am getting the following error when trying to run dsTwo.data[‘a’] = “something”;

VM61:1 Uncaught TypeError: Cannot read property ‘data’ of undefined
at :1:7
(anonymous) @ VM61:1

I assume that something with Chrome and the way it interprets JS changed since this book was written.

I forgot the new keyword when invoking the constructor through the console. D’oh!