He really loves eslint. First there was jslint by Douglas Crockford, then jshint. Eslint is even more flexible and pluggable. You can have custom rules. He loves tuning the rules.

There are presets that you can base off, and extend. He too, likes to leave off semicolons!

what is use strict and should he use it everywhere?

On Node 6 it's already in strict mode. But if you send stuff to older browsers, then it can save you from some bugs. Later Babel will add this automatically.