keyboard.js

var Keyboard = new Class({
    prebind: 'handler',

    initialize: function() {
      $(document).on({
        keypress: this.handler,
        keyup:    this.handler
      });
    },

    handler: function(event, flag) {
      (this._keys || (this._keys = {}))[
        String.fromCharCode(event.keyCode)
      ] = event.type === 'keypress';
    },

    isPressed: function(key) {
      return this._keys[key];
    }
});