Common or Core where put my file?

I have been reading this post Common vs Core - difference

But I can not understand, what is understood as a conceptually central code?

Really, what should I put in Core and what in common?

I have a file js as a library with some functions, example of my archive

const getType = v =>
      v === undefined ? 'undefined' : v === null ? 'null' : v.constructor.name.toLowerCase();
const arrayMin = arr => Math.min(...arr);

Where should put my file, Common or Core and why?