How to define setter/getter on prototype

Using an object literal declaration (simplest way):

var o = {
    a: 7,
    get b() {
        return this.a + 1;
    },
    set c(x) {
        this.a = x / 2
    }
};

Using Object.defineProperty (on modern browsers that support ES5):

Object.defineProperty(o, "myProperty", {
    get: function myProperty() {
        // code
    }
});

Or using __defineGetter__ and __defineSetter__ (DEPRECATED):

var d = Date.prototype;
d.__defineGetter__("year", function() { return this.getFullYear(); });
d.__defineSetter__("year", function(y) { this.setFullYear(y); });

Use Object.defineProperty() on Subclass.prototype. There are also __defineGetter__ and __defineSetter__ available on some browsers, but they are deprecated. For your example, it would be:

Object.defineProperty(Subclass.prototype, "myProperty", {
    get: function myProperty() {
        // code
    }
});