Constructs a new AbstractKeyboard. Subclasses should call this to get a basic keyboard before extending it with a concrete implementation. Subclasses should pass in an object as $protected, which will be populated with keydown(key) and keyup(keydownId), which allow keyboards to simulate a key being pressed or released. key is either a printable character or one of the constants that is in AbstractKeyboard.KEYS to represent special keys: TAB, BACKSPACE, ENTER, LEFT, and RIGHT. keydown returns an id that can be passed to keyup to mark that key as released.

AbstractKeyboards are not frozen, so you can subclass AbstractKeyboard using parasitic inheritance:

function MySpecialKeyboard() {
    var $protected = {};
    var self = AbstractKeyboard($protected);

    self.pressAKeyRepeatedly = function(key, numTimes) {
        for(var i = 0; i < numTimes; i++) {
            $protected.keyup($protected.keydown(key));
        }
    };

    Object.freeze(self);
    return self;
}