interface Article {
   title: string;
   body: string;
}

function isArticle(body: unknown): body is Article {
  let b = body as Article;
  return !!b && typeof b.body === 'string' && typeof b.title === 'string';
}

interface Article {
   title: string;
   body: string;
}

function isArticle(body: unknown): body is Article {
  let b = body as Article;
  return !!b && typeof b.body === 'string' && typeof b.title === 'string';
}