In compose_state.js, there is the export object that many other classes reference. That has the variable subject that needs to be changed to topic.
See UML
Many classes will need to be changed (compose_actions.js etc) and it will most probably require many tests to be updated.
First change the exports.subject -> exports.topic and then one global search and replace (cmd+shift+f in Sublime of Atom) will of compose_state.subject -> compose_state.topic will do the trick here. @eywoon
In compose_state.js, there is the export object that many other classes reference. That has the variable subject that needs to be changed to topic. See UML
Many classes will need to be changed (compose_actions.js etc) and it will most probably require many tests to be updated.