TommosTools

contexto

Caveats

This page contains notes on a few inconvenient or possibly surprising behaviours associated with the Contexto library

Imperative updates cannot be applied to the default context value

During development, useContextUpdate will throw an error if it is called without an appropriate Provider above it in the component tree. In a production environment it will silently fail.

Changing the value prop also causes an update

Although the value prop in a Contexto Provider is not the “single source of truth”, it can be used to update the value. The most recent update “wins”, regardless of whether the update was imperative or prop-based.

This behaviour can be avoided by initialising the Provider using initialValue instead of value. This may be preferable in some cases e.g. to avoid memoising the initial value.

Hot Reloading/Fast Refresh doesn’t know about imperative updates

In a development environment, React’s various tools for fast refresh do their best to maintain state during code updates, but they have no insight into the internal state of components.

By default, Fast Refresh on a Contexto-powered app will default back to the context values as determined by the value/initialValue props on each Provider. To avoid this problem, make sure to always specify an arbitrary (but consistent) contextId when calling createContext:

const MyUserContext = createContext(defaultValue, { contextId: "Main user context" });

Contexto assumes that contexts created with the same contextId are the same context, so make sure your ids are unique!

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