Cleanup

From review of PR #56 (watch2 support), I have a feeling that we should be able to clean up both the source code and all of the tests. I am raising this for future consideration and discussion.

Starting to add a list:

- [ ] use const & let instead of var, especially in new code (noticed after merging PR #56)
- [ ] look for ways to make the code easier to read & understand, especially the code added in PRs #56 & #76

/cc @l3ender

Review PR #56 and PR #76 first, then inspect the source code and tests affected by their changes. Turn the broad cleanup request into specific readability and var-to-const/let tasks, with each task identifying its code and tests and defining the expected completed state.

Written by the indexing model from the issue text.