__defineGetter__, __defineSetter__ – JavaScript, AJAX, jQuery – Fórum – Programujte.com

http://developer.mozilla.org/en/docs/Core_JavaScript_1.5_Guide:Working_with_Objects#Defining_Getters_and_Setters

o = {

  a:7,

  get b() { return this.a+1; },

  set c(x) { this.a = x/2; }

};



o.c = 10;

document.write(o.b);