Konami Code

konami.js

function konamiCode(cb) {
  const UP = 38;
  const DOWN = 40;
  const LEFT = 37;
  const RIGHT = 39;
  const KONAMI_CODE = [UP, UP, DOWN, DOWN, LEFT, RIGHT, LEFT, RIGHT].join('-');
  let keypresses = [];
  let enabled = false;
  let rootEl = null;
  let passive = false;

  try {
    const options = {
      get passive() {
        passive = true;
      }
    };
    window.addEventListener("test", options, options);
    window.removeEventListener("test", options, options);
  } catch(err) {
    passive = false;
  }

  function handler(event) {
    keypresses.push(event.keyCode);

    if (keypresses.length === 8) {
      if (keypresses.join('-') === KONAMI_CODE) {
        cb();
        keypresses = [];
      } else {
        keypresses = keypresses.slice(1, 8);
      }
    }
  }
  
  window.addEventListener('keydown', handler, passive ? { passive: true } : false);
  
  return function() {
    window.removeEventListener('keydown', handler);
  };
}