chain_subscribeFinalizedHeads

Description

Subscribe to real‑time chain updates over WebSocket. Use to stream new or finalized heads or runtime version changes into your app.

Emits new finalized block headers. Requires WebSocket.

JavaScript (polkadot.js)

import { ApiPromise, WsProvider } from '@polkadot/api';

const api = await ApiPromise.create({ provider: new WsProvider(S.wsBase) });
const unsub = await api.rpc.chain.subscribeFinalizedHeads((header) => {
  console.log('finalized #', header.number.toString());
});
// Later: await unsub();