# H3Event

> H3Event, carries incoming request, prepared response and context.

With each HTTP request, H3 internally creates an `H3Event` object and passes it though event handlers until sending the response.

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An event is passed through all the lifecycle hooks and composable utils to use it as context.

**Example:**

```js
app.get("/", async (event) => {
  // Log HTTP request
  console.log(`[${event.req.method}] ${event.req.url}`);

  // Parsed URL and query params
  const searchParams = event.url.searchParams;

  // Try to read request JSON body
  const jsonBody = await event.req.json().catch(() => {});

  return "OK";
});
```

## `H3Event` Methods

### `H3Event.waitUntil`

Tell the runtime about an ongoing operation that shouldn't close until the promise resolves.

```js [app.mjs]
import { logRequest } from "./tracing.mjs";

app.get("/", (event) => {
  request.waitUntil(logRequest(request));
  return "OK";
});
```

```js [tracing.mjs]
export async function logRequest(request) {
  await fetch("https://telemetry.example.com", {
    method: "POST",
    body: JSON.stringify({
      method: request.method,
      url: request.url,
      ip: request.ip,
    }),
  });
}
```

## `H3Event` Properties

### `H3Event.app?`

Access to the H3 [application instance](/guide/api/h3).

### `H3Event.context`

The context is an object that contains arbitrary information about the request.

You can store your custom properties inside `event.context` to share across utils.

**Known context keys:**

- `context.params`: Matched router parameters.
- `middlewareParams`: Matched middleware parameters
- `matchedRoute`: Matched router route object.
- `sessions`: Cached session data.
- `basicAuth`: Basic authentication data.

### `H3Event.req`
Incoming HTTP request info based on native [Web Request](https://developer.mozilla.org/en-US/docs/Web/API/Request) with additional runtime addons (see [srvx docs](https://srvx.h3.dev/guide/handler#extended-request-context)).

```ts
app.get("/", async (event) => {
  const url = event.req.url;
  const method = event.req.method;
  const headers = event.req.headers;

  // (note: you can consume body only once with either of this)
  const bodyStream = await event.req.body;
  const textBody = await event.req.text();
  const jsonBody = await event.req.json();
  const formDataBody = await event.req.formData();

  return "OK";
});
```

### `H3Event.url`

Access to the full parsed request [URL](https://developer.mozilla.org/en-US/docs/Web/API/URL).

### `H3Event.res`

Prepared HTTP response status and headers.

```ts
app.get("/", (event) => {
  event.res.status = 200;
  event.res.statusText = "OK";
  event.res.headers.set("x-test", "works");

  return "OK";
});
```

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