Method check

third_party/subscriptions-project/config.js:691–714

* @return {?PageConfig}

()

   * @return {?PageConfig}
   */
  check() {
    // Already resolved.
    if (!this.configResolver_) {
      return null;
    }
    const config =
      this.metaParser_.check() ||
      this.ldParser_.check() ||
      this.microdataParser_.check();
    if (config) {
      // Product ID has been found: initialize the rest of the config.
      this.configResolver_(config);
      this.configResolver_ = null;
    } else if (this.doc_.isReady()) {
      this.configResolver_(
        Promise.reject(
          user().createError('No config could be discovered in the page')
        )
      );
      this.configResolver_ = null;
    }
    debugLog(config);
    return config;
  }
}

class TypeChecker {