Using the converter allows you to specify generic type arguments whenstoring and retrieving objects from Firestore.

example

class Post {constructor(readonly title:string, readonly author:string) {}  toString():string {returnthis.title +', by ' +this.author;  }}const postConverter = {  toFirestore(post: Post): firebase.firestore.DocumentData {return {title: post.title, author: post.author};  },  fromFirestore(    snapshot: firebase.firestore.QueryDocumentSnapshot,    options: firebase.firestore.SnapshotOptions  ): Post {const data = snapshot.data(options)!;returnnew Post(data.title, data.author);  }};const postSnap =await firebase.firestore()  .collection('posts')  .withConverter(postConverter)  .doc().get();const post = postSnap.data();if (post !==undefined) {  post.title;// string  post.toString();// Should be defined  post.someNonExistentProperty;// TS error}