Implementation of ES5 Object.getPrototypeOf in terms of __proto__

gistfile1.js

// Copied from Effective Javascript (by David Herman)
// Item 31: Prefer Object.getPrototypeOf to __proto__
// For JS environments that do not provide the ES5 API, it is easy to implement
// in terms of __proto__

if (typeof Object.getPrototypeOf === "undefined" ) {
  Object.getPrototypeOf = function(obj) {
    var t = typeof obj;
    if (!obj || (t !== "object" && t != "function")) {
      throw new TypeError("not an object");
    }
    return obj.__proto__;
  };
}