createPocketPlane - a way to create getters/setters using an internal slot!

pocketplane.js

// Pocket Plane - 2013 (c) Brendan Molloy - CC0 License

function createPocketPlane(object, prop, fallback) {
    Object.defineProperty(object, prop, {
        get: pocketPlane,
        set: pocketPlane,
        configurable: true
    });

    function pocketPlane() {
        var val;

        Object.defineProperty(this, prop, {
            set: magic,
            get: magic
        });

        return magic.apply(this, arguments);

        function magic() {
            if (arguments.length > 0) {
                val = arguments[0];
            } else {
                return val === undefined ? fallback : val;
            }
        }
    }
}