Create a property accessor for `Object.prototype.foo` and create `{foo: bar}` to see whether `foo`'s setter being called or not

object.prototype.foo.accessor.js

// I tested this in Node.js and Chrome browser

'use strict'

// Set things up
Object.defineProperty(Object.prototype, 'foo', {
  set (x) {
    console.log('Setter is called: ' + x)
    this._foo = x
  },
  get () {
    console.log('Getter is called: ' + this._foo)
    return this._foo
  },
  enumerable: false,
  configurable: false
})

console.log('Own property (root): ' + Object.prototype.hasOwnProperty('foo')) // true

// Assigning property 'foo'
const obja = {}
obja.foo = 'obja' // Setter is called: obja
obja.foo // Getter is called: obja
console.log('Own property (obja): ' + obja.hasOwnProperty('foo')) // false

// Initializing property 'foo'
const objb = {foo: 'objb'} // No effect, it's not assigning, it doesn't call foo's setter
objb.foo // Still no effect
console.log('Own property (objb): ' + objb.hasOwnProperty('foo')) // true

// As you can see, 'foo' is nothing like '__proto__'.
// While initializing '__proto__' in object literal results an object with chosen proto, initializing 'foo' has no special effect
// So I think '__proto__' must be treated specially, which implies that V8 is aware of '__proto__'
// Do you think that V8 was going to call '__proto__' setter and getter to reduce its efficiency? I think not
// I think that V8 was "Object.create(__proto__)" before caring about other properties
// 'foo = {abc: 123, __proto__: bar}' is more like 'foo = object extends bar {abc: 123}'