Object.getPrototypeOf(obj)

​​Object.getPrototypeOf(obj)​​ 

• 返回指定对象的原型（内部​​[[Prototype]]​​属性的值）。
• obj：要返回其原型的对象。
• 返回值：给定对象的原型。如果没有继承属性，则返回 null 。

var proto = {};
var obj = Object.create(proto);
Object.getPrototypeOf(obj) === proto; // true

var reg = /a/;
Object.getPrototypeOf(reg) === RegExp.prototype; // true
Object.getPrototypeOf(new Date()) === Date.prototype // true

一些注意点

console.log(Object.getPrototypeOf(Object) === Function.prototype)
console.log(Object.getPrototypeOf(Function) === Function.prototype)
console.log(Object.getPrototypeOf(Date) === Function.prototype)
console.log(Object.getPrototypeOf(Object()) === Object.prototype)
console.log(Object.getPrototypeOf(Function()) === Function.prototype)
console.log(Object.getPrototypeOf(Date()) === String.prototype)
console.log(Object.getPrototypeOf(new Object()) === Object.prototype)
console.log(Object.getPrototypeOf({}) === Object.prototype)
console.log(Object.getPrototypeOf(new Function()) === Function.prototype)
console.log(Object.getPrototypeOf(new Date()) === Date.prototype)
console.log({} == new Object())