EventSource server-sent events API definition
EventSource is a server-sent event API that allows a server to push events to a client. The EventSource object connects to a server over HTTP and receives events in a text-based format.
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eventsource
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EventSource constructor syntax
EventSource is created with the constructor `new EventSource(url, options)` where url is a USVString representing the URL to connect to, and options is an optional EventSourceInit dictionary containing optional settings.
EventSource fetcher option for Workers bindings
The EventSource constructor accepts a `fetcher` option to use a different fetch implementation, such as one provided by a Cloudflare Workers binding. This is specified as `{ fetcher: env.MYFETCHER }` and is a Cloudflare Workers specific extension. By default, EventSource uses the global `fetch()` function under the covers.
EventSource url property
The `eventSource.url` property is a read-only USVString that returns the URL of the event source.
EventSource readyState property
The `eventSource.readyState` property is a read-only USVString that indicates the state of the connection.
EventSource withCredentials property
The `eventSource.withCredentials` property is a read-only Boolean that indicates whether the EventSource object was instantiated with cross-origin (CORS) credentials set (`true`), or not (`false`).
EventSource close method
The `eventSource.close()` method closes the connection.
EventSource event handlers
EventSource has three event handler properties: `onopen` called when a connection is opened, `onmessage` called when a message is received, and `onerror` called when an error occurs.
EventSource events
EventSource fires three events: `open` fired when the connection is opened, `message` fired when a message is received, and `error` fired when an error occurs.
EventSource.from class method
EventSource.from(readableStream) is a Cloudflare Workers specific extension that creates a new EventSource object from an existing ReadableStream. This instance does not initiate a new connection but instead attaches to the provided stream.