Fetching data from Firestore sequentially.

jspromise2_option1.js

// https://firebase.google.com/docs/firestore/quickstart
var db = firebase.firestore();

async function fetchArticle(articleId, authorId) {
  try {
    // get author and article docs sequentially
    const authorSnap = await db.doc("authors/" + authorId).get();
    const articleSnap = await db.doc("articles/" + articleId).get();
  }
  catch (err) {/* handle error */}

  // extract data
  const authorData = authorSnap.data();
  const articleData = articleSnap.data();

  // save to state
  this.setState({authorData, articleData});
}