# React useEventSource Hook: Server-Sent Events with Auto-Reconnect (2026)

> Source: <https://dev.to/childrentime/react-useeventsource-hook-server-sent-events-with-auto-reconnect-2026-fbm>
> Published: 2026-08-12 07:06:05+00:00

Live notifications, deployment logs, stock tickers, AI responses streaming in token by token — none of these need a WebSocket. They're all one-directional: the server talks, the client listens. The browser has had a native protocol for exactly this since 2011 — **Server-Sent Events (SSE)** — and it runs over plain HTTP, passes through proxies and load balancers untouched, and reconnects automatically when the connection drops.

What SSE *doesn't* have is a good React story. The native `EventSource`

API is imperative: you construct it, attach listeners, and must tear it down at exactly the right moment — the classic effect-lifecycle minefield. [ useEventSource](https://reactuse.com/browser/useeventsource/) from

`@reactuses/core`

`data`

, `status`

, and `error`

your component just renders. This post covers the hook's full API, the reconnect behavior that native `EventSource`

gets subtly wrong, and `useFetchEventSource`

`Authorization`

header or a POST body, which in 2026 means every AI-completions endpoint.

```
npm install @reactuses/core
js
import { useEventSource } from "@reactuses/core";

function DeploymentLog() {
  const { data, status } = useEventSource("/api/deploy/stream");

  return (
    <div>
      <span>{status === "CONNECTED" ? "🟢 live" : "🟡 connecting…"}</span>
      <pre>{data}</pre>
    </div>
  );
}
```

That's a complete live-updating component. The hook opens the connection on mount, updates `data`

on every message, exposes the connection lifecycle as `status`

(`"CONNECTING" | "CONNECTED" | "DISCONNECTED"`

), and closes the stream when the component unmounts. No refs, no listeners, no cleanup function to forget.

Server-Sent Events is just an HTTP response that never finishes. The server replies with `Content-Type: text/event-stream`

and writes messages as plain text, separated by blank lines:

```
data: {"price": 101.42}
id: 7

event: trade
data: {"symbol": "ACME", "qty": 200}
id: 8
```

Three field types matter:

`data:`

— the payload (always a string; JSON-encode structured data yourself).`event:`

— an optional event `id:`

— an optional event ID. The browser remembers the last one and sends it back as a `Last-Event-ID`

header when it reconnects, so a well-built server can resume where the client left off.Because it's plain HTTP, SSE works through corporate proxies, CDNs, and HTTP/2 multiplexing without the upgrade-handshake drama WebSockets sometimes hit. The trade-off: it's server → client only, and the native browser API can only send GET requests with no custom headers. Keep that limitation in mind — it's the reason the second hook in this post exists.

Wiring `EventSource`

by hand looks manageable:

```
// ⚠️ hand-rolled — three bugs waiting to happen
function Ticker() {
  const [price, setPrice] = useState<string | null>(null);

  useEffect(() => {
    const es = new EventSource("/api/prices");
    es.onmessage = e => setPrice(e.data);
    return () => es.close();
  }, []);

  return <span>{price}</span>;
}
```

The problems show up in production, not in the demo:

`EventSource`

retries forever, silently. If your API is down, every open tab hammers it every few seconds until the heat death of the universe — and you have no state telling the UI "we're offline" so you can show a banner or give up.`onerror`

gives you a bare `Event`

— no status code, no reason. If you don't track connection state yourself, your UI happily shows stale data as if it were live.`event: trade`

line requires its own `addEventListener("trade", …)`

`removeEventListener`

in cleanup. Miss one and you leak listeners across React 18 StrictMode's mount-unmount-mount cycle.None of this is hard, exactly. It's just easy to get 90% right — which is the worst kind of wrong.

Everything the manual version does badly, as returned state:

```
const { data, event, status, error, lastEventId, open, close, eventSourceRef } =
  useEventSource(url, events?, options?);
```

`data: string | null`

`event: string | null`

`status`

`"CONNECTING" | "CONNECTED" | "DISCONNECTED"`

. Render it; that's your live-indicator.`error: Event | null`

`lastEventId: string | null`

`id:`

field of the last message, i.e. your resume cursor.`open()`

/ `close()`

`close()`

is `open()`

reconnects and resets the retry counter.`eventSourceRef`

`EventSource`

instance if you need it.Pass the event names you care about as the second argument, and the hook registers — and cleans up — every listener for you:

```
const { data, event } = useEventSource("/api/stream", ["trade", "quote"]);

// event === "trade" | "quote" | null — which channel data came from
useEffect(() => {
  if (event === "trade") appendTrade(JSON.parse(data!));
}, [data, event]);
```

The `autoReconnect`

option replaces `EventSource`

's silent infinite retry with a policy you choose:

```
const { status } = useEventSource("/api/notifications", [], {
  autoReconnect: {
    retries: 5,        // give up after 5 attempts (or pass a () => boolean)
    delay: 2000,       // wait 2s between attempts
    onFailed: () => toast.error("Live updates unavailable — refresh to retry"),
  },
});
```

`retries`

defaults to `-1`

(retry forever, matching native behavior), but now it's a *decision* rather than a surprise, and `onFailed`

gives you the moment to tell the user. Pair it with `status === "DISCONNECTED"`

to render a degraded-mode UI instead of silently stale numbers.

By default the hook connects on mount. Pass `immediate: false`

to wait for user intent:

```
const { status, open, close } = useEventSource("/api/live-scores", [], {
  immediate: false,
});

<button onClick={status === "CONNECTED" ? close : open}>
  {status === "CONNECTED" ? "Pause live scores" : "Go live"}
</button>
```

Here is the native API's dirty secret: `new EventSource(url)`

**cannot send custom headers**. No `Authorization: Bearer …`

, no `X-Api-Key`

, nothing. Your options with the native API are cookies (`withCredentials: true`

) or a token in the query string — one of which doesn't work cross-domain with modern cookie policies, and the other of which lands your token in every access log between the browser and your server.

It also can't POST. That matters because the biggest SSE consumers of 2026 — OpenAI-style AI completion endpoints — are all `POST /v1/chat/completions`

with a JSON body and a bearer token, streaming back `text/event-stream`

. The native `EventSource`

API literally cannot call them.

[ useFetchEventSource](https://reactuse.com/browser/usefetcheventsource/) solves this by speaking SSE over

`fetch`

(built on Microsoft's battle-tested `fetch-event-source`

``` js
import { useFetchEventSource } from "@reactuses/core";

const { data, status, error } = useFetchEventSource("/api/v1/chat/completions", {
  method: "POST",
  headers: { Authorization: `Bearer ${token}` },
  body: JSON.stringify({ model: "gpt-5", messages, stream: true }),
  autoReconnect: { retries: 3, delay: 1000 },
});
```

Same return shape as `useEventSource`

— `data`

, `event`

, `status`

, `error`

, `lastEventId`

, `open`

, `close`

— so switching between the two is a one-line change, not a rewrite.

The `onMessage`

callback is the natural place to accumulate a streamed completion:

```
function Answer({ prompt }: { prompt: string }) {
  const [text, setText] = useState("");

  const { status } = useFetchEventSource("/api/ask", {
    method: "POST",
    headers: { Authorization: `Bearer ${token}` },
    body: JSON.stringify({ prompt }),
    onMessage: msg => {
      if (msg.data === "[DONE]") return;
      const delta = JSON.parse(msg.data).choices[0]?.delta?.content ?? "";
      setText(prev => prev + delta);
    },
    onError: err => {
      if (isRateLimit(err)) return 5000; // return a number = retry after N ms
    },
  });

  return <Markdown>{text}{status === "CONNECTED" && "▌"}</Markdown>;
}
```

Two details worth stealing: returning a number from `onError`

overrides the reconnect delay for that attempt (perfect for `Retry-After`

-style backoff), and the functional `setText(prev => …)`

update means token order survives React's batching.

`useEventSource` |
|---|

`useFetchEventSource`

`EventSource`

`fetch`

+ stream parser`Last-Event-ID`

resumeSimple rule: start with `useEventSource`

; the moment you type the word `Authorization`

, switch.

`EventSource`

/`fetch`

only inside effects, so they render harmlessly on the server — no `typeof window`

guards in your code. First paint shows `status: "DISCONNECTED"`

, then the client connects.`useDocumentVisibility`

`close()`

when hidden and `open()`

on return — the `Last-Event-ID`

handshake makes resume cheap.`useBroadcastChannel`

`useNetwork`

`useOnline`

`fetch`

. SSE earns its keep only when the stream outlives the request.`fetch`

instead of base64-ing it through a text stream.`Last-Event-ID`

— right for every server-to-client feed.`useEventSource`

`EventSource`

lifecycle into rendered state (`data`

/ `status`

/ `error`

), handles named-event listener cleanup, and replaces invisible infinite retry with a reconnect policy you set — `retries`

, `delay`

, `onFailed`

.`EventSource`

can't send an `Authorization`

header or a POST body. `useFetchEventSource`

`close()`

means `open()`

resets the retry budget. Wire them to visibility and network state for streams that behave like a good citizen.`useEventSource`

, `useFetchEventSource`

, and 110+ other SSR-safe, TypeScript-first hooks live in [ @reactuses/core](https://reactuse.com) — one install, tree-shakeable, no dependencies to babysit.

```
npm install @reactuses/core
```