javascript isnative ()

/**
   * Gets the native function at `key` of `object`.
   *
   * @private
   * @param {Object} object The object to query.
   * @param {string} key The key of the method to get.
   * @returns {*} Returns the function if it's native, else `undefined`.
   */
  function getNative(object, key) {
   var value = object == null ? undefined : object[key];
   return isNative(value) ? value : undefined;
  }
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