createSelector

Accepts one or more "input selectors" (either as separate arguments or a single array), a single "result function", and an optional options object, and generates a memoized selector function.

The Redux docs usage page on Deriving Data with Selectors covers the purpose and motivation for selectors, why memoized selectors are useful, and typical Reselect usage patterns.

const selectTodosByCategory = createSelector(
  [
    // Pass input selectors with typed arguments
    (state: RootState) => state.todos,
    (state: RootState, category: string) => category
  ],
  // Extracted values are passed to the result function for recalculation
  (todos, category) => {
    return todos.filter(t => t.category === category)
  }
)

Parameters

Name	Description
inputSelectors	An array of input selectors, can also be passed as separate arguments.
resultFunc	A function that takes the results of the input selectors as separate arguments.
createSelectorOptions?	An optional options object that allows for further customization per selector.

Returns

A memoized output selector.

Output Selector Fields

The output selectors created by createSelector have several additional properties attached to them:

Name	Description
resultFunc	The final function passed to createSelector.
memoizedResultFunc	The memoized version of resultFunc.
lastResult	Returns the last result calculated by memoizedResultFunc.
dependencies	The array of the input selectors used by createSelector to compose resultFunc.
recomputations	Counts the number of times memoizedResultFunc has been recalculated.
resetRecomputations	Resets the count of recomputations count to 0.
dependencyRecomputations	Counts the number of times the input selectors (dependencies) have been recalculated. This is distinct from recomputations, which tracks the recalculations of the result function.
resetDependencyRecomputations	Resets the dependencyRecomputations count to 0.
memoize	Function used to memoize the resultFunc.
argsMemoize	Function used to memoize the arguments passed into the output selector.

Type Parameters

Name	Description
InputSelectors	The type of the input selectors array.
Result	The return type of the result function as well as the output selector.
OverrideMemoizeFunction	The type of the optional memoize function that could be passed into the options object to override the original memoize function that was initially passed into createSelectorCreator.
OverrideArgsMemoizeFunction	The type of the optional argsMemoize function that could be passed into the options object to override the original argsMemoize function that was initially passed into createSelectorCreator.