React 18

• Leverage new React 18 APIs for improved safety and optimizations. (#1488)
• Fixes for <StrictMode> (#1473, #1444, #1509).
• Experimental support for useTransition() using hooks with _TRANSITION_SUPPORT_UNSTABLE suffix. (#1572, #1560)
• Recoil updates now re-render earlier:
  • Recoil and React state changes from the same batch now stay in sync. (#1076)
  • Renders now occur before transaction observers instead of after.

New Features

• Add refresh() to the useRecoilCallback() interface for refreshing selector caches. (#1413)
• Callbacks from selector's getCallback() can now mutate, refresh, and transact Recoil state, in addition to reading it, for parity with useRecoilCallback(). (#1498)
• Recoil StoreID's for <RecoilRoot> and Snapshot stores accessible via useRecoilStoreID() hook (#1417) or storeID parameter for atom effects (#1414).
• RecoilLoadable.all() and RecoilLoadable.of() now accept either literal values, async Promises, or Loadables. (#1455, #1442)
• Add .isRetained() method for Snapshots and check if snapshot is already released when using .retain() (#1546)

Other Fixes and Optimizations

• Reduce overhead of snapshot cloning
  • Only clone the current snapshot for callbacks if the callback actually uses it. (#1501)
  • Cache the cloned snapshots from callbacks unless there was a state change. (#1533)
• Fix transitive selector refresh for some cases (#1409)
• Fix some corner cases with async selectors and multiple stores (#1568)
• Atom Effects
  • Run atom effects when atoms are initialized from a set during a transaction from useRecoilTransaction_UNSTABLE() (#1466, #1569)
  • Atom effects are cleaned up when initialized by a Snapshot which is released. (#1511, #1532)
  • Unsubscribe onSet() handlers in atom effects when atoms are cleaned up. (#1509)
  • Call onSet() when atoms are initialized with <RecoilRoot initializeState={...} > (#1519, #1511)
• Avoid extra re-renders in some cases when a component uses a different atom/selector. (#825)
• <RecoilRoot> will only call initializeState() once during the initial render. (#1372)
• Lazily compute the properties of useGetRecoilValueInfo_UNSTABLE() and Snapshot#getInfo_UNSTABLE() results (#1549)
• Memoize the results of lazy proxies. (#1548)

Breaking Changes

• Rename atom effects from effects_UNSTABLE to just effects, as the interface is mostly stabilizing. (#1520)
• Atom effect initialization takes precedence over initialization with <RecoilRoot initializeState={...} >. (#1509)
• useGetRecoilValueInfo_UNSTABLE() and Snapshot#getInfo_UNSTABLE() always report the node type. (#1547)
• The 0.3 release introduced the need to retain Snapshots for later use, but it was mostly a warning. Now it is necessary to retain a Snapshot for asynchronous selectors to resolve. See the documentation here and here. Future releases will further enforce this as garbage collection is released.