A while ago I switched the project from JSHint to ESLint (the latter being better-maintained and offering more features). However, I set many of the settings as warnings because I didn't have time to address potential issues. Nor did I really have time to tweak linting for settings that make the code more maintainable.

So, the task would essentially be to look at ESLint warnings, and see what can be safely addressed. (For example, a lot of the == equality warnings may not be "fixable" to === without testing for every value that passes through that check.) It would be helpful to also set warnings for things to address in the future / ongoing, such as enforcing JSDoc documentation.