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Unlock the Craic: The Konami Code in TypeScript

This is a placeholder. The full article is published on Medium.

↑ ↑ ↓ ↓ ← → ← → B A

If you recognise that sequence, you already know where this is going.

The Konami Code has been a video game easter egg since 1986. It started as a cheat code in Gradius and became a cultural shorthand for hidden things, for people who look for them. Building one into your own site is partly a technical exercise and mostly an act of personality.

The core logic

Detecting a key sequence in TypeScript is straightforward: maintain a buffer of recent keypresses, compare it against the target sequence after every key event, and clear the buffer when it either matches or diverges beyond recovery.

const KONAMI = ['ArrowUp','ArrowUp','ArrowDown','ArrowDown',
                 'ArrowLeft','ArrowRight','ArrowLeft','ArrowRight',
                 'b','a'];

let buffer: string[] = [];

window.addEventListener('keydown', (e) => {
  buffer.push(e.key);
  buffer = buffer.slice(-KONAMI.length);
  if (buffer.join(',') === KONAMI.join(',')) {
    activate();
  }
});

What you do with it

That part is up to you. Redirect, reveal, transform. The mechanism is the same; the payoff is whatever you decide is worth finding.

Read the full piece on Medium.

— Matt Kaszubski