A very straightforward example of leveraging the konami code (uses isEqual from lodash because it reads easier)

konami-code.js

const konamiCode = [38, 38, 40, 40, 37, 39, 37, 39, 66, 65, 13]
let konamiTracker = []

const listener = event => {
  const key = event.keyCode

  const currentSequence = [...konamiTracker, key]
  const slice = konamiCode.slice(0, currentSequence.length)
  const isPartialMatch = _.isEqual(currentSequence, slice)
  const isExactMatch = _.isEqual(currentSequence, konamiCode)

  konamiTracker = isPartialMatch ? konamiTracker.concat([key]) : []
  if (isExactMatch) console.log('execute the thing')
}

window.konami = window.addEventListener('keydown', listener)