LazySequenceclass

Sequence of values that calls a StartCallback when it has iterators that are iterating, and calls the corresponding StopCallback when all iterators have finished.

• The start callback runs lazily on the first active iterator and the returned stop callback runs when the last iterator finishes.

A ThroughSequence paired with a start/stop callback. The StartCallback runs when the first iterator begins iterating; the StopCallback it returns runs when the last iterator finishes. This is the sequence equivalent of an observable subscription — work happens only while something is listening.

Usage

Pass a source iterator and a start callback. The callback sets up the work and returns a teardown function:

import { DeferredSequence, LazySequence } from "shelving/sequence";

const deferred = new DeferredSequence<number>();

const seq = new LazySequence(deferred, () => {
  const id = setInterval(() => deferred.resolve(Date.now()), 500);
  return () => clearInterval(id); // StopCallback — runs when the last iterator finishes.
});

for await (const ts of seq) {
  console.log(ts); // the interval runs only for the duration of this loop
}