JavaScript KeyEvent keyCode helper library

KeyMan.js

var Keyman = (function() {
    var Key = {
        8: 'BACKSPACE',
        9: 'TAB',
        13: 'ENTER',
        16: 'SHIFT',
        17: 'CTRL',
        18: 'ALT',
        19: 'PAUSE_BREAK',
        20: 'CAPS_LOCK',
        27: 'ESCAPE',
        33: 'PAGE_UP',
        34: 'PAGE_DOWN',
        35: 'END',
        36: 'HOME',
        37: 'LEFT_ARROW',
        38: 'UP_ARROW',
        39: 'RIGHT_ARROW',
        40: 'DOWN_ARROW',
        45: 'INSERT',
        46: 'DELETE',
        48: [0,')'],
        49: [1,'!'],
        50: [2,'@'],
        51: [3,'#'],
        52: [4,'$'],
        53: [5,'%'],
        54: [6,'^'],
        55: [7,'&'],
        56: [8,'*'],
        57: [9,'('],
        65: 'A',
        66: 'B',
        67: 'C',
        68: 'D',
        69: 'E',
        70: 'F',
        71: 'G',
        72: 'H',
        73: 'I',
        74: 'J',
        75: 'K',
        76: 'L',
        77: 'M',
        78: 'N',
        79: 'O',
        80: 'P',
        81: 'Q',
        82: 'R',
        83: 'S',
        84: 'T',
        85: 'U',
        86: 'V',
        87: 'W',
        88: 'X',
        89: 'Y',
        90: 'Z',
        91: 'LEFT_WINDOW_KEY',
        92: 'RIGHT_WINDOW_KEY',
        93: 'SELECT_KEY',
        96: 'NUM_PAD_0',
        97: 'NUM_PAD_1',
        98: 'NUM_PAD_2',
        99: 'NUM_PAD_3',
        100: 'NUM_PAD_4',
        101: 'NUM_PAD_5',
        102: 'NUM_PAD_6',
        103: 'NUM_PAD_7',
        104: 'NUM_PAD_8',
        105: 'NUM_PAD_9',
        106: 'NUM_PAD_ASTERISK',
        107: 'NUM_PAD_PLUS',
        109: 'NUM_PAD_MINUS',
        111: 'NUM_PAD_FOWARD_SLASH',
        112: 'F1',
        113: 'F2',
        114: 'F3',
        115: 'F4',
        116: 'F5',
        117: 'F6',
        118: 'F7',
        119: 'F8',
        120: 'F9',
        121: 'F10',
        122: 'F11',
        123: 'F12',
        144: 'NUM_LOCK',
        145: 'SCROLL_LOCK',
        186: [';',':'],
        187: ['=','+'],
        188: [',','<'],
        189: ['-','_'],
        190: ['.','>'],
        191: ['/','?'],
        192: ['`','~'],
        219: ['[','{'],
        220: ['\\','|'],
        221: [']','}'],
        222: ['\'','"']
    }

    var lastpressed         = [],
        currentlyPressed    = [],
        shift               = false;

    function isArray(obj) {
        return Array.prototype.isPrototypeOf(obj);
    }

    function toChar(keycode) {
        var shift   = !~currentlyPressed.indexOf(/shift/i),
            char    = (shift && isArray(char) ? char[1] : char[0]);

        return shift ? char : char.toLowerCase();
    }

    document.addEventListener('keydown', function(e) {
        var char = toChar(e.keyCode);

        currentlyPressed.push(char);

        e.xchar     = char;
        e.xallChars = currentlyPressed;
    }, true);

    document.addEventListener('keyup', function(e) {
        e.xchar     = currentlyPressed.splice(toChar(e.keyCode), 1)[0];
        e.xallChars = currentlyPressed;
    }, true);

    return {
        toChar      : toChar,
        addToString : addToString
    }
})();