キーボードイベントを参照

So, event.code may match a wrong character for unexpected layout. Same letters in different layouts may map to different physical keys, leading to different codes. Luckily, that happens only with several codes, e.g. keyA , keyQ , keyZ (as we’ve seen), and doesn’t happen with special keys such as Shift . You can find the list in the
英語を使う国のキーボードとドイツのキーボードのレイアウトが違うのでevent.コード値は同じですが、イベントです.key値が異なる現象が発生します.
event.code値自体は、英米のキーボードレイアウトに関連付けられています.
Preventing the default action on keydown can cancel most of them, with the exception of OS-based special keys. For instance, on Windows Alt+F4 closes the current browser window. And there’s no way to stop it by preventing the default action in JavaScript.
OSベースのキーオフイベントはeventです.防ぎきれない

event.重要な例

switch (event.key) {
    case "Down": // IE/Edge specific value
    case "ArrowDown":
      // Do something for "down arrow" key press.
      break;
    case "Up": // IE/Edge specific value
    case "ArrowUp":
      // Do something for "up arrow" key press.
      break;
    case "Left": // IE/Edge specific value
    case "ArrowLeft":
      // Do something for "left arrow" key press.
      break;
    case "Right": // IE/Edge specific value
    case "ArrowRight":
      // Do something for "right arrow" key press.
      break;
    case "Enter":
      // Do something for "enter" or "return" key press.
      break;
    case "Esc": // IE/Edge specific value
    case "Escape":
      // Do something for "esc" key press.
      break;
    default:
      return; // Quit when this doesn't handle the key event.
  }