watch [JavaScript snippet]

function main() {

  var obj = {};

  obj.watch("foo", function(elem_name, old_value, new_value) {

    txt_out("elem_name: " + elem_name + ", old_value: " + old_value + ", new_value: " + new_value);
    return new_value.toUpperCase();
  });


  obj.foo = "foo";
  obj.bar = "bar";

  txt_out("---");

  txt_out("foo: " + obj.foo);
  txt_out("bar: " + obj.bar);
}