As covered in the section there are three JSON files which are needed for the addon to work. They handle your state definition, communication between the addon and Squirrel and how to display the property panel in the designer.
defaultState.json
The default state is a JSON representation of the data model you want Squirrel to use when it saves a project with your addon in, and when it adds your addon to the Squirrel canvas for the first time.
This JSON object is available inside your addon via the getter this returns a copy of the state object. To set properties of state you need to send the data to Squirrel using the method. If the property you are updating has been bound to a spreadsheet cell in Squirrel, the data you pass will be inserted into the relevant cell(s).
messageBindings.json
This file lets Squirrel know whether the property in defaultState in the addon is to be used to:
send data from the addon to Squirrel,
receive data from Squirrel into the addon or
both send and receive data
propertyPanel.json
This file contains a JSON representation of the property panel. You create the panel using a collection of pre-defined available.
