API · Create
fromEvent()
Adapt repeated browser or Node events into a hot Exstream source with explicit overflow policy.
Signature
fromEvent<Args extends unknown[], T>(
target: EventTargetLike | EventEmitterLike,
event: string | symbol,
options?: FromEventOptions<Args, T> | null,
): Exstream<T, RecordContext<T>> & { received: number }
interface FromEventOptions<Args extends unknown[], T> extends StreamOptions {
map?: (...args: Args) => T
end?: string | symbol | false
error?: string | symbol | false
highWaterMark?: number
}Example
const messages = exstream.fromEvent(socket, 'message', {
map: (event) => event.data,
end: 'close',
error: 'error',
highWaterMark: 256,
overflow: 'drop-oldest',
})Parameters
target must expose addEventListener/removeEventListener or on/off. event is the data event. By default, one event argument becomes the value and multiple arguments become an array; map replaces that rule. end defaults to 'end', error to 'error', and either can be false to disable its listener.
highWaterMark is the source buffer limit: default 1 for targets with pause/resume, otherwise 1024. Non-pausable targets must use a finite limit. Although FromEventOptions extends StreamOptions, the adapter uses highWaterMark rather than bufferLimit; setting only bufferLimit has no effect. overflow defaults to 'error'; drop policies are appropriate only when event loss is intentional. signal comes from StreamOptions.
Hot-source behavior
received counts data events before mapping, including events later dropped or failed. Pausable targets are paused when writeData() reports pressure and resumed on drain. Non-pausable targets keep producing into the configured buffer. A mapping exception or configured error event is a fatal source failure. End, destroy, or abort removes every listener.