portfolio/packages/frptools/docs/stream.md

stream

A stream is a computed that works asynchronously. Dependencies can be synchronous or asynchronous functions returning a scalar or a promise respectively. Also calling a stream multiple overlapping times will return the same promise and result (so long as dependencies do not change in the time gap). In this way, stream can serve as a temporal deduplicator.

Usage

Creation

const getToken = stream(
	async tokenUrl => fetch(tokenUrl), // computation function
	[getTokenUrl, tokenTimeout] // array of subscribable dependencies
);

Read

if (await getToken()) {
	/* do stuff with the token */
}

Provide a hash function for complex result types

When the stream result is a type that is not determined to be equal with simple equality (===), provide a hash function to the hashableStream type to create a stream that will reduce the result value to a value that can be compared with the identity operator before comparison. The computed result value will still be stored unmodified.

const tokenStream = hashableStream(token => token && token.id);

const getToken = tokenStream(async tokenUrl => fetch(tokenUrl), [getTokenUrl]);