Reselect is a selector library for Redux that creates memoized functions to compute derived data from application state.
The problem Reselect solves is the need to efficiently compute derived values from Redux state without unnecessary recalculations. It works by accepting input selectors that extract values from state and a result function that transforms those values. When the output selector is called, it only recalculates if its input values have changed, returning the same reference when no recalculation occurs. This reference stability is particularly important for libraries like React that rely on reference equality to optimize rendering.
Reselect is useful for any Redux application where you need to derive computed values from state, though it works with any plain JavaScript immutable data structure. It is already included by default in Redux Toolkit, so no separate installation is needed for projects using that package. The library provides multiple APIs including createSelector for basic memoized selectors, createSelectorCreator for custom memoization strategies, createStructuredSelector for object-shaped selectors, and alternative memoization options like lruMemoize and weakMapMemoize. Developers should adopt it when they want to avoid redundant computations and ensure that derived data maintains reference equality across renders.
The project maintains rapid responsiveness to user reports and contributions, with maintainers typically addressing new issues and pull requests within hours. Nearly all open issues originate from outside users rather than the core team, reflecting a substantial base of real-world adopters. Development work concentrates on TypeScript improvements, caching enhancements, and documentation refinements.
