(Currently you'll need Google Chrome Canary for this to work. Make sure to set the Enable Experimental JavaScript flag from chrome://flags and restart the browser.)

An object o is created and Object.observe() is called on it.

Three changes are made to o and Object.observe() records these changes as shown below.

Use the console to find out what happens if you make further changes to o: it's defined in global scope.

Call Object.unobserve(o, observer) to stop observing changes.

View source on github