let F = function (n) { this.a = n }
let f = function () { return this.a }
let fs = function () { "use strict"; return this.a }
let value = new F(12)
value.a
f()
fs()
fs.call({ a: 11, b: 22 })
F(99)
a
let obj = Object.create({ f })
obj
obj.a = "yeah"
obj
obj.f()

Object.getOwnPropertyNames(obj)
Object.getOwnPropertyNames(Object.getPrototypeOf(obj))