Channel module

Usage

npm i -E @prelude/channel
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import * as Ch from '@prelude/channel'
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Reading and completion

• read() returns the next value and throws Channel closed. after completion.
• next() returns the complete iterator result. A value has done: false; completion has done: true.
• maybeRead() returns the next value or undefined after completion.

When a channel can contain undefined, maybeRead() cannot distinguish a queued undefined value from completion because both produce undefined. Use next() and inspect its done property when that distinction matters.

Failure

• fail(err) closes the channel and rejects pending and subsequent reads with err; failed and error expose the state.
• ofIterable() and ofAsyncIterable() fail their channel when the source throws, so consumers see the error instead of a silent completion.

Cancellation

read, maybeRead, write, maybeWrite and writeIgnore take { signal }; select, selectNext and selectAsync take { signal } as their first argument; after, ofIterable and ofAsyncIterable take it in a trailing options object.

• Aborting a pending read or write withdraws it — nothing is consumed or delivered — and rejects it with signal.reason; a write that was already accepted (buffered or handed to a reader) is unaffected.
• Aborting a select withdraws every attempt and rejects (the select generator throws) with signal.reason.
• Aborting after, ofIterable or ofAsyncIterable fails the channel with signal.reason, so readers reject and the producer stops.

const controller = new AbortController()
const value = await ch.read({ signal: controller.signal })
for await (const value of Ch.select({ signal: controller.signal }, a, b)) { ... }
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Closing a channel (close, closeWriting, breaking out of for await) remains the way to stop all readers and writers.

License

This package is dedicated to the public domain under CC0 1.0.