function starBlogArticle(articleId: string): firebase.firestore.WriteBatch {
  const batch = firebase.firestore().batch();
	
  batch.set(...); // Some changes
  batch.update(...);
  
  return batch;
}

function createBlogArticle(articleId: string, title: string): firebase.firestore.WriteBatch {
  const batch = firebase.firestore().batch();
	
  batch.set(...);
  batch.set(...);
  
  return batch;
}

...

// On the application side

const onClickCreate = () => {
  const articleId = '...';
  const batch = createBlogArticle(articleId, title);
  batch.merge(starBlogArticle(articleId));

  batch.commit();
}