keyboard.js

var Keyboard = new Class({
    initialize: function() {
        var scope = this;
        this._keys = {};

        var handler = function(e, flag) {
            scope._keys[String.fromCharCode(e.which)] = flag;
        }

        $(document).on('keypress', handler, true).on('keyup', handler, false);
    },
    isPressed: function(key) {
        if (key in this._keys) {
            return this._keys[key];
        }
    }
});