v8.1.0

[markerikson]

This feature release adds new development-mode safety checks for common errors (like poorly-written selectors), adds a workaround to fix crash errors when React-Redux hooks are imported into React Server Component files, and updates our hooks API docs page with improved explanations and updated links.

Changelog

Development Mode Checks for useSelector

We've had a number of users tell us over time that it's common to accidentally write selectors that have bad behavior and cause performance issues. The most common causes of this are either selectors that unconditionally return a new reference (such as state => state.todos.map() without any memoization ), or selectors that actually return the entire root state ( state => state ).

We've updated useSelector to add safety checks in development mode that warn if these incorrect behaviors are detected:

• Selectors will be called twice with the same inputs, and useSelector will warn if the results are different references
• useSelector will warn if the selector result is actually the entire root state

By default, these checks only run once the first time useSelector is called. This should provide a good balance between detecting possible issues, and keeping development mode execution performant without adding many unnecessary extra selector calls.

If you want, you can configure this behavior globally by passing the enum flags directly to <Provider>, or on a per-useSelector basis by passing an options object as the second argument:

// Example: globally configure the root state "noop" check to run every time
<Provider store={store} noopCheck="always">
  {children}
</Provider>

// Example: configure `useSelector` to specifically run the reference checks differently:
function Component() {
  // Disable check entirely for this selector
  const count = useSelector(selectCount, { stabilityCheck: 'never' })
  // run once (default)
  const user = useSelector(selectUser, { stabilityCheck: 'once' })
  // ...
}

This goes along with the similar safety checks we've added to Reselect v5 alpha as well.

Context Changes

We're still trying to work out how to properly use Redux and React Server Components together. One possibility is using RTK Query's createApi to define data fetching endpoints, and using the generated thunks to fetch data in RSCs, but it's still an open question.

However, users have reported that merely importing any React-Redux API in an RSC file causes a crash, because React.createContext is not defined in RSC files. RTKQ's React-specific createApi entry point imports React-Redux, so it's been unusable in RSCs.

This release adds a workaround to fix that issue, by using a proxy wrapper around our singleton ReactReduxContext instance and lazily creating that instance on demand. In testing, this appears to both continue to work in all unit tests, and fixes the import error in an RSC environment. We'd appreciate further feedback in case this change does cause any issues for anyone!

We've also tweaked the internals of the hooks to do checks for correct <Provider> usage when using a custom context, same as the default context checks.

Docs Updates

We've cleaned up some of the Hooks API reference page, and updated links to the React docs.

What's Changed

• check for Provider even when using custom context by @EskiMojo14 in check for Provider even when using custom context #1990
• Add a stability check, to see if selector returns stable result when called with same parameters. by @EskiMojo14 in Add a stability check, to see if selector returns stable result when called with same parameters. #2000
• Add an E2E-ish test that verifies behavior when imported into RSCs by @markerikson in Add an E2E-ish test that verifies behavior when imported into RSCs #2030
• lazily create Context for RSC compat by @phryneas in lazily create Context for RSC compat #2025
• Add warning for selectors that return the entire state by @EskiMojo14 in Add warning for selectors that return the entire state #2022

Full Changelog: v8.0.7...v8.1.0

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This discussion was created from the release v8.1.0.