Optional
onMessage: (msg: EventSourceMessage) => voidA function that will be called on each message.
Optional
onId: (id: string) => voidA function that will be called on each id
field.
Optional
onRetry: (retry: number) => voidA function that will be called on each retry
field.
A function that should be called for each incoming line buffer.
Parses line buffers into EventSourceMessages.