Would you consider it mandatory to have explaination for the items that you use to be a good programmer for 'this' need? For example what if the candidate doesn't know exactly what is the purpose of 'use strict' but always uses it in the program to avoid any messages.

Would you hire a programmer 1. having good practices ie.. using knowledge for programming advantage, or 2. expert in theory to which programmer may not be capable of converting it into practice.

In my opinion many of the 'know how' is not readily transferable to information. But for human being it can be easily seen by someone having similar or better knowledge.