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redux-toolkitcreateReducerintermediate

createReducer with Builder

📖 Usage Example
const { createReducer, createAction } = ReduxToolkit
const inc = createAction('inc')
const reducer = createReducer(0, builder => {
  builder.addCase(inc, state => state + 1)
})
reducer(0, inc()) // → 1

createReducer with the builder API provides full type safety and a clean pattern for handling multiple actions.

createReducer with Builder

createReducer(initialState, builder => ...) defines a reducer using a builder callback. Call builder.addCase(actionCreator, handler) to handle specific actions.

Challenge: Use createReducer with the builder API to handle increment, decrement, and addBy.

counterReducer(0, increment())   // → 1
counterReducer(5, decrement())   // → 4
counterReducer(0, addBy(10))     // → 10
💡 Hints (3)
  • • Chain `.addCase()` calls on the builder object.
  • • The handler receives `(state, action)` — return a new value or mutate with Immer.
  • • Unhandled actions automatically return the current state.