sugar/common/internal/hasValidPlainObjectPrototype.js

A Javascript utility library for working with native objects.

'use strict';

var coreUtilityAliases = require('../var/coreUtilityAliases');

var hasOwn = coreUtilityAliases.hasOwn;

function hasValidPlainObjectPrototype(obj) {
  var hasToString = 'toString' in obj;
  var hasConstructor = 'constructor' in obj;
  // An object created with Object.create(null) has no methods in the
  // prototype chain, so check if any are missing. The additional hasToString
  // check is for false positives on some host objects in old IE which have
  // toString but no constructor. If the object has an inherited constructor,
  // then check if it is Object (the "isPrototypeOf" tapdance here is a more
  // robust way of ensuring this if the global has been hijacked). Note that
  // accessing the constructor directly (without "in" or "hasOwnProperty")
  // will throw a permissions error in IE8 on cross-domain windows.
  return (!hasConstructor && !hasToString) ||
          (hasConstructor && !hasOwn(obj, 'constructor') &&
           hasOwn(obj.constructor.prototype, 'isPrototypeOf'));
}

module.exports = hasValidPlainObjectPrototype;