# stream

A `stream` is a [computed](./computed.md) 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

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

Note: Property and container dependencies are "locked" while the computation function is run. If
there are any out-of-band updates to a dependency, the value will be set but will not propagate
until after the computation function is complete and the stream's subscribers are notified.

### Read

```js
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.

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

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