title: How to build a Firestore query chain based on a dynamic response from a promise
body: <p>Let's say I need to query Firestore against a collection of subjects that I receive in a promise:</p>
  
  <pre><code>const subjects: string[] = await getSubjects(); //response: ['Math', 'Science', 'History'];
  </code></pre>
  
  <p>Since I don't know how many subjects might be returned in the promise at any given time, how would I go about dynamically generating the chain below so I can properly query Firestore?</p>
  
  <pre><code>ref.where('subject[subjects[0].toLowerCase()]', '==' , true)
      .where('subject[subjects[1].toLowerCase()]', '==' , true)
      .where('subject[subjects[2].toLowerCase()]', '==' , true);
  </code></pre>
  
  <p>The more subjects that are returned, the more <code>.where()</code> methods it would need to generate.</p>