Enforced getters and setters in JavaScript?

gistfile1.js

var o = (function(){
    var properties = {
        color  : { value: "red" },
        size   : { value: "large", set: false },
        secret : { value: "cookies", get: false }
    };
    return {
        // this only exists in Mozilla?
        __noSuchMethod__: function (name, args) {
            // the name argument is the called method
            var action = name.substr(0,3);
            // we only handle getters and setters
            if ((action !== "get") && (action !== "set")) { return; }
            // there must be a property name
            if (name.length < 4) { return; }
            // allow camel case by lowercasing all property names
            var key = name.substr(3).toLowerCase();
            // only use existing properties
            if (!(key in properties)) { return; }
            if (action === "set") {
                // did we get any arguments?
                if (args.length < 1) { return; }
                if (("set" in properties[key]) && (properties[key].set === false)) {
                    console.warn("Attempt to write to a read-only property: " + key);
                } else {
                    properties[key].value = args[0];
                }
                // allow chaining
                return this;
            } else {
                // must be a getter
                if (("get" in properties[key]) && (properties[key].get === false)) {
                    console.warn("Attempt to read from a write-only property: " + key);
                    return;
                }
                return properties[key].value;
            }
        } 
    };
})();
console.log(o.getColor()); // should say "red"
console.log(o.setColor("blue").getColor()); // should say "blue"
console.log(o.getColor()); // should say "blue"
// these are not allowed so we should get a warning
console.log(o.setSize("big").getSize());
o.setSecret("cupcake").getSecret();