Real-Time

Firestore has one of the most convenient real-time APIs in web and mobile development. We write a listener: import { collection, onSnapshot, query, where } from "firebase/firestore"; const q = query( collection(db, "messages"), where("roomId", "==", "general") ); const unsubscribe = onSnapshot(q, (snapshot) => { snapshot.docChanges().forEach((change) => { console.log(change.type, change.doc.id, change.doc.data()); }); }); After that, the UI updates whenever matching documents are added, modified, or removed. It feels similar to a WebSocket because the browser receives real-time updates without manually polling. But Firestore listeners and WebSockets are not the same abstraction. ...

Most web applications start with a simple request-response model. The browser asks for something, the server responds, and the connection is done. That model works well for pages, APIs, forms, dashboards, and most CRUD applications. But some features need something different: chat messages that appear instantly live sports scores multiplayer game state collaborative editing cursors trading prices delivery tracking real-time notifications terminal sessions in the browser For these features, repeatedly asking the server “anything new?” becomes wasteful and slow. ...