lodash/internal/shimIsPlainObject.js

define(['./baseForIn', './isObjectLike'], function(baseForIn, isObjectLike) {

  /** `Object#toString` result references. */
  var objectTag = '[object Object]';

  /** Used for native method references. */
  var objectProto = Object.prototype;

  /** Used to check objects for own properties. */
  var hasOwnProperty = objectProto.hasOwnProperty;

  /**
   * Used to resolve the `toStringTag` of values.
   * See the [ES spec](https://people.mozilla.org/~jorendorff/es6-draft.html#sec-object.prototype.tostring)
   * for more details.
   */
  var objToString = objectProto.toString;

  /**
   * A fallback implementation of `_.isPlainObject` which checks if `value`
   * is an object created by the `Object` constructor or has a `[[Prototype]]`
   * of `null`.
   *
   * @private
   * @param {*} value The value to check.
   * @returns {boolean} Returns `true` if `value` is a plain object, else `false`.
   */
  function shimIsPlainObject(value) {
    var Ctor;

    // Exit early for non `Object` objects.
    if (!(isObjectLike(value) && objToString.call(value) == objectTag) ||
        (!hasOwnProperty.call(value, 'constructor') &&
          (Ctor = value.constructor, typeof Ctor == 'function' && !(Ctor instanceof Ctor)))) {
      return false;
    }
    // IE < 9 iterates inherited properties before own properties. If the first
    // iterated property is an object's own property then there are no inherited
    // enumerable properties.
    var result;
    // In most environments an object's own properties are iterated before
    // its inherited properties. If the last iterated property is an object's
    // own property then there are no inherited enumerable properties.
    baseForIn(value, function(subValue, key) {
      result = key;
    });
    return typeof result == 'undefined' || hasOwnProperty.call(value, result);
  }

  return shimIsPlainObject;
});