Fetching data from Firestore simultaneously.

jspromise2_option2.js

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

async function fetchArticle(articleId, authorId) {
  
  // get author and article docs simultaneously
  const authorPromise = db.doc("authors/" + authorId).get();
  const articlePromise = db.doc("articles/" + articleId).get();
  
  // wait until both compleeted
  try {
    const [authorSnap, articleSnap] = await Promise.all([authorPromise, articlePromise]);
  }
  catch (err) {/* handle error */}

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

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