O.o() quick example

Oo.js

var records = [];
var obj = {};
var obj2 = {};

function observer(r){
  [].push.apply(records, r);  
  console.log(r);
}

Object.observe(obj, observer); // Begin observing changes

obj.foo = 41; // triggers a new notification (name: foo, type: "new", object {foo: 41})
obj2.foo = 42; // does not trigger a notification
obj.foo = 43; // triggers an update notification (name: foo, type: "updated", oldValue: 41, object {foo: 43})

Object.unobserve(obj, observer); // Stop observing changes

obj.foo = 44; // does not trigger a notification