Javascript 捕捉键盘代码时发出键盘错误声音

我正在用Javascript编程，它可以捕获键盘输入，但问题是每次用户按下一个键都会发出错误的声音。如何禁用它

@Polaris878

function KeyPressed(e)
{
    if (!e) e = window.event;
    if (e.which)
    {
        keycode = e.which
    }
    else if (e.keyCode)
    {
        keycode = e.keyCode
    }
    switch (keycode)
    {
    case 49:
        key = "1";
        break;
    case 50:
        key = "2";
        break;
    case 51:
        key = "3";
        break;
    case 52:
        key = "4";
        break;
    case 53:
        key = "5";
        break;
    case 54:
        key = "6";
        break;
    case 55:
        key = "7";
        break;
    case 56:
        key = "8";
        break;
    case 57:
        key = "9";
        break;
    case 48:
        key = "0";
        break;
    default:
        key = "";
        return false;
        break
    }
    if (keys == "NULL")
    {
        keys = key
    }
    else
    {
        keys = keys + key
    } if (keys.length >= 5)
    {
        document.formular.submit();
    }
    document.formular.code.value = keys;
}
var keys = "";
document.onkeydown = KeyPressed

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您是否介意向我们展示捕获按键/按下事件的JavaScript代码？@Polaris878给您↓