hello.js

const fs = require('fs')

fs.readFile('hello.txt', 'utf8', (error, content) =>
  content
    .split('\n')
    .filter(line => line.includes('dog'))
    .forEach(line => console.log(line))
)

hello.txt

fluffykins is a dragon
wolfbane is a dragon
kittylunch is a cat
karo is a dog
multidog is a dog

Wish you kept the finished product before you refactor. Maybe push when you finish it in the original context and then when you refactor push a new commit, then we can come here and review them side by side. That would be so awesome, because I find I learn lots by looking at them side by side.
You are a great teacher and so easy to listen too!!