get-proto 
Robustly get the Prototype of an object. Uses the best available method.
Getting started
npm install --save get-proto
Usage/Examples
const assert = require('assert');
const getProto = require('get-proto');
const a = { a: 1, b: 2, [Symbol.toStringTag]: 'foo' };
const b = { c: 3, __proto__: a };
assert.equal(getProto(b), a);
assert.equal(getProto(a), Object.prototype);
assert.equal(getProto({ __proto__: null }), null);
Tests
Clone the repo, npm install, and run npm test