useEventSource

See: EventSource or Server-Sent-Events connection to an HTTP server, which sends events in text/event-stream format.

Types

UseEventSourceProps

• @template T Expected type of the parsed message data.

Configuration object accepted by useEventSource.

Property	Type	Required	Description
url	string \| URL		URL of the SSE endpoint. Can be set here or passed to open() at connection time. If omitted, open() must always be called with a URL.
opts	EventSourceInit		Options forwarded to the EventSource constructor. The most useful option is { withCredentials: true } for cross-origin SSE endpoints that require cookies or HTTP auth.
events	{ name: string; handler?: (evt: MessageEvent) => void }[]		Array of named events to listen to on the EventSource. Each entry registers a listener for the named event type alongside the default "message" listener.
immediateConnection	boolean		When true, the EventSource connection is opened immediately on mount. When false (default), call open() to connect.
onOpen	(evt: Event) => void		Called when the EventSource connection is established (open event).
onError	(evt: Event) => void		Called when an error occurs on the EventSource connection (error event). This includes connection errors and server-side errors.
onMessage	<T>(evt: MessageEvent<T>) => void		Called for every unnamed "message" event received from the server.

UseEventSourceResult

• @template T Expected type of the parsed message data.

Result object returned by useEventSource.

Property	Type	Required	Description
status	"READY" \| "CONNECTING" \| "OPENED" \| "CLOSED"	✓	Current connection state of the EventSource: - "READY" — not yet connected (initial state). - "CONNECTING" — connection attempt in progress. - "OPENED" — connection established, receiving events. - "CLOSED" — connection closed (manually or by the server).
data	T \| null	✓	The most recently received "message" event data. null before the first message arrives.
open	(url?: string) => void	✓	Opens the EventSource connection to the provided (or configured) URL.
close	() => void	✓	Closes the EventSource connection. The status transitions to "CLOSED".