Konami Code Easter Egg

konamify.js

// Insert this into your already sourced JS file, or link to it in the HEAD of your DOM.
// Add whatever you like to the keystroke keychain match.
document.addEventListener('DOMContentLoaded', () => {
    'use strict';

    // Standard Konami Code keystroke chain.
    // Up Up Down Down Left Right Left Right B A Start
    konamify("arrowuparrowuparrowdownarrowdownarrowleftarrowrightarrowleftarrowrightbaenter");
});

function konamify(code) {
    let buffer = [];
    let lastKeyTime = Date.now();

    document.addEventListener('keydown', event => {
        const key = event.key.toLowerCase();

        const currentTime = Date.now();

        if (currentTime - lastKeyTime > 1000) {
            buffer = [];
        }

        lastKeyTime = currentTime;
        buffer.push(key);
        if (buffer.join('') === code) {
            // Konamified.
            console.log('Konamified');
            // Your Konami Code action here.
        }
    });
}