31. WebSockets for live data

Unlike request/response HTTP, a WebSocket keeps one connection open in both directions, letting a node push events as they happen — new blocks, pending transactions, contract event logs — instead of the client polling.

js
import WebSocket from "ws";

const ws = new WebSocket(process.env.WS_RPC_URL);

ws.on("open", () => {
  ws.send(JSON.stringify({
    jsonrpc: "2.0", id: 1, method: "eth_subscribe", params: ["newHeads"],
  }));
});

ws.on("message", (data) => {
  const msg = JSON.parse(data.toString());
  if (msg.method === "eth_subscription") {
    console.log("new block:", msg.params.result.number);
  }
});

WebSocket connections need reconnection logic: networks drop, nodes restart, and a production service must detect a closed socket and re-subscribe rather than silently going quiet.

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