var book = {
_year:2004,
edition: 1
};
Object.defineProperty(book, "year", {
get: function() {
return this._year;
},
set: function(newValue) {
if (newValue > 2004) {
this._year += newValue;
this.edition += newValue - 2004;
}
}
});
book.year = 2006;
console.log(book.edition);