## ReconnectingWebSocket.onopen property

An event listener to be called when the WebSocket connection's readyState changes to OPEN; this indicates that the connection is ready to send and receive data.

**Signature:**

```typescript
onopen: ((event: Event) => void) | null;
```

- [ReconnectingWebSocket.onopen property](/content/docs/sdk/core.reconnectingwebsocket.onopen#reconnectingwebsocketonopen-property/index.html)