Return a value from variable (?)

I don’t know too much JS and I’m trying to return a value from a code for another thing to work.
(Basically, I’m using a module called aoi.js to make a discord bot, and I am trying to get the file count in a folder.)
I could only get this code to work, and it only logs to the console:

const fs = require('fs');
const dir = './commands/$getVar[category]';

fs.readdir(dir, (err, files) => {

I need to return (?) “files.length” as a raw text (?) instead of logging it.

Could anyone help me with this issue?