polyfill `event.key` for Chrome (and other non-Firefox browsers) - named keys

eventKeyPolyfill.js

// Disclaimer: for now, this works for only US ASCII keyboards.
var KEYCODES_TO_KEYS = {
  3: 'Cancel',
  6: 'Help',
  8: 'Backspace',
  9: 'Tab',
  12: 'Clear',
  13: 'Enter',
  16: 'Shift',
  17: 'Control',
  18: 'Alt',
  19: 'Pause',
  20: 'CapsLock',
  27: 'Escape',
  28: 'Convert',
  29: 'NonConvert',
  30: 'Accept',
  31: 'ModeChange',
  33: 'PageUp',
  34: 'PageDown',
  35: 'End',
  36: 'Home',
  37: 'ArrowLeft',
  38: 'ArrowUp',
  39: 'ArrowRight',
  40: 'ArrowDown',
  41: 'Select',
  42: 'Print',
  43: 'Execute',
  44: 'PrintScreen',
  45: 'Insert',
  46: 'Delete',
  48: ['0', ')'],
  49: ['1', '!'],
  50: ['2', '@'],
  51: ['3', '#'],
  52: ['4', '$'],
  53: ['5', '%'],
  54: ['6', '^'],
  55: ['7', '&'],
  56: ['8', '*'],
  57: ['9', '('],
  91: 'OS',
  93: 'ContextMenu',
  144: 'NumLock',
  145: 'ScrollLock',
  181: 'VolumeMute',
  182: 'VolumeDown',
  183: 'VolumeUp',
  186: [';', ':'],
  187: ['=', '+'],
  188: [',', '<'],
  189: ['-', '_'],
  190: ['.', '>'],
  191: ['/', '?'],
  192: ['`', '~'],
  219: ['[', '{'],
  220: ['\\', '|'],
  221: [']', '}'],
  222: ["'", '"'],
  224: 'Meta',
  225: 'AltGraph',
  246: 'Attn',
  247: 'CrSel',
  248: 'ExSel',
  249: 'EraseEof',
  250: 'Play',
  251: 'ZoomOut',
};

var i = 0;

// Function keys (F1-24).
for (i = 1; i < 25; i++) {
  KEYCODES_TO_KEYS[111 + i] = 'F' + i;
}

// Printable ASCII characters.
var letter = '';
for (i = 65; i < 91; i++) {
  letter = String.fromCharCode(i);
  KEYCODES_TO_KEYS[i] = [letter.toLowerCase(), letter.toUpperCase()];
}


// Polyfill `key` on `KeyboardEvent`.
var testKeyboardEvent = new KeyboardEvent('keydown');
if (!('key' in testKeyboardEvent)) {
  Object.defineProperty(KeyboardEvent.prototype, 'key', {
    get: function (x) {
      var key = KEYCODES_TO_KEYS[this.which || this.keyCode];

      if (Array.isArray(key)) {
        key = key[+this.shiftKey];
      }

      return key;
    }
  });
}


window.addEventListener('keydown', function (e) {
  console.log(e);
});