# `watchFor`
This is a utility for watching an expression until its output satisfies a condition.

=== "JSX"
	```jsx
	import { watchFor } from "rvx/async";

	// Wait for an expression to return a truthy result:
	await watchFor(() => signal.value > 42);

	// Wait for an expression to match a condition and get the matching expression result:
	const value = await watchFor(signal, value => value > 42);
	```

=== "No Build"
	```jsx
	import { watchFor } from "./rvx.async.js";

	// Wait for an expression to return a truthy result:
	await watchFor(() => signal.value > 42);

	// Wait for an expression to match a condition and get the matching expression result:
	const value = await watchFor(signal, value => value > 42);
	```

## Timeouts
When a timeout is specified and exceeded, a `WatchForTimeoutError` is thrown:

=== "JSX"
	```jsx
	// Use a timeout of 2000 milliseconds:
	await watchFor(signal, value => value > 42, 2000);
	```

=== "No Build"
	```jsx
	// Use a timeout of 2000 milliseconds:
	await watchFor(signal, value => value > 42, 2000);
	```

By default, no timeout is used and the returned promise will never resolve if the condition is never met.