Without running this code could you tell me its output?

gistfile1.js

Object.defineProperty(Object.prototype, "foo", {
    set: function (v) {
        console.log("hello:", v);
    },

    configurable: true}
);

var obj = { foo: "bar" };
var obj2 = {};
obj2.foo = "bar2";

hello:bar2

(EDIT: removed the space. Twas a typo.)

Defining in literal never fallbacks to prototype, it's always about setting own properties. var obj = { foo: "bar" } is same as:

var obj = Object.create(Object.prototype, {
  foo: { value: 'bar', configurable: true, enumerable: true, writable: true }
}))