gistfile1.js

Object.extend = Object.extend.wrap(function(proceed, destination, source, safe) {
  if (!safe) return proceed(destination, source);
  for (var property in source) {
    if (!(property in destination))
      destination[property] = source[property]; 
  }
  return destination;
});

Object.extend({foo: 123}, {foo: 456}, true).foo
// -> 123