Uncaught ReferenceError: todo is not defined

Hi, everyone.
I have followed the installation guide on ionic to build a project called “todo”.
I started to code on it and I tried to run it on Chrome. I checked on the console that there is a few errors as the following:

controller.js:1 Uncaught ReferenceError: todo is not defined(…)(anonymous function) @
ionic.bundle.js:25005 GET 404 (Not Found)

Is these two error fatal that I should rebuild another projects for continuing coding? Because I have tried to apply a number of changes on it like adding an accordion list and retrieving data from json but seems they didn’t work normally.

Would anyone please help? As I am really new to ionic and I have encountered too much errors. Sigh. Thank you so much!