How to deal with the situation where your boss insists on something weird ?

We are in front end team and build our product based on ReactJS. My boss told me that she could not figure out how to execute iterate by map or forEach. She insists on writing iterate by for-loop.

What JavaScript testing framework should I use?

I would like to kickstart implementing a JavaScript testing framework in my project. Which one should I use? Mocha or Karma? Or is there something better?

As a front end developer, should I focus on rapid revolution of front end development or get familiar with backend development stuff?