makeRW

function makeRW(obj, field) {
    var val = obj[field];
    Object.defineProperty(obj, field, {
        get: function() {
            return this['rw_' + field];
        },
        set: function(val) {
            this['rw_' + field] = val;
        }
    });
    obj['rw_' + field] = val;
};