Is there any way to prevent replacement of JavaScript object properties?

I would like to make an object's structure immutable, preventing its properties from being subsequently replaced. The properties need to be readable, however. Is this possible?

I'm sure there are no language features (along the lines of final in Java and readonly in C#) to support this but wondered whether there might be another mechanism for achieving the same result?

I'm looking for something along these lines:

var o = {
    a: "a",
    f: function () {
        return "b";
    }
};

var p = o.a;        // OK
o.a = "b";          // Error
var q = o.f();      // OK
o.f = function () { // Error
    return "c"; 
};