# Response
> H3 response utilities.
## Event Stream
### `createEventStream(event, opts?)`
Initialize an EventStream instance for creating [server sent events](https://developer.mozilla.org/en-US/docs/Web/API/Server-sent_events/Using_server-sent_events)
**Example:**
```ts
import { createEventStream, sendEventStream } from "h3";
app.get("/sse", (event) => {
const eventStream = createEventStream(event);
// Send a message every second
const interval = setInterval(async () => {
await eventStream.push("Hello world");
}, 1000);
// cleanup the interval and close the stream when the connection is terminated
eventStream.onClosed(async () => {
console.log("closing SSE...");
clearInterval(interval);
await eventStream.close();
});
return eventStream.send();
});
```
## Sanitize
### `sanitizeStatusCode(statusCode?, defaultStatusCode)`
Make sure the status code is a valid HTTP status code.
### `sanitizeStatusMessage(statusMessage)`
Make sure the status message is safe to use in a response.
Allowed characters: horizontal tabs, spaces or visible ascii characters: [https://www.rfc-editor.org/rfc/rfc7230#section-3.1.2](https://www.rfc-editor.org/rfc/rfc7230#section-3.1.2)
## Serve Static
### `serveStatic(event, options)`
Dynamically serve static assets based on the request path.
## More Response Utils
### `html(first)`
### `iterable(iterable)`
Iterate a source of chunks and send back each chunk in order. Supports mixing async work together with emitting chunks.
Each chunk must be a string or a buffer.
For generator (yielding) functions, the returned value is treated the same as yielded values.
**Example:**
```ts
return iterable(async function* work() {
// Open document body
yield "\nExecuting...
\n";
// Do work ...
for (let i = 0; i < 1000; i++) {
await delay(1000);
// Report progress
yield `- Completed job #`;
yield i;
yield `
\n`;
}
// Close out the report
return `
`;
});
async function delay(ms) {
return new Promise((resolve) => setTimeout(resolve, ms));
}
```
### `noContent(status)`
Respond with an empty payload.
**Example:**
```ts
app.get("/", () => noContent());
```
### `redirect(location, status, statusText?)`
Send a redirect response to the client.
It adds the `location` header to the response and sets the status code to 302 by default.
In the body, it sends a simple HTML page with a meta refresh tag to redirect the client in case the headers are ignored.
**Example:**
```ts
app.get("/", () => {
return redirect("https://example.com");
});
```
**Example:**
```ts
app.get("/", () => {
return redirect("https://example.com", 301); // Permanent redirect
});
```
### `redirectBack(event)`
Redirect the client back to the previous page using the `referer` header.
If the `referer` header is missing or is a different origin, it falls back to the provided URL (default `"/"`).
By default, only the **pathname** of the referer is used (query string and hash are stripped) to prevent spoofed referers from carrying unintended parameters. Set `allowQuery: true` to preserve the query string.
**Security:** The `fallback` value MUST be a trusted, hardcoded path — never use user input. Passing user-controlled values (e.g., query params) as `fallback` creates an open redirect vulnerability.
**Example:**
```ts
app.post("/submit", (event) => {
// process form...
return redirectBack(event, { fallback: "/form" });
});
```
### `writeEarlyHints(event, hints)`
Write `HTTP/1.1 103 Early Hints` to the client.
In runtimes that don't support early hints natively, this function falls back to setting response headers which can be used by CDN.