Function simple

test/typescript/reducers.ts:16–59

* Simple reducer definition with no action shape checks. * Uses string comparison to determine action type. * * `AnyAction` type is used to allow action property access without requiring * type casting.

()

 * type casting.
 */
function simple() {
  type State = number

  const reducer: Reducer<State> = (state = 0, action) => {
    if (action.type === class="st">'INCREMENT') {
      const { count = 1 } = action
      if (typeof count === class="st">'number') {
        return state + count
      }
    }

    if (action.type === class="st">'DECREMENT') {
      const { count = 1 } = action
      if (typeof count === class="st">'number') {
        return state + count
      }
    }

    return state
  }

  class="cm">// Reducer function accepts any object with `type` prop as action.
  class="cm">// Any extra props are allowed too.
  let s: State = reducer(undefined, { type: class="st">'init' })
  s = reducer(s, { type: class="st">'INCREMENT' })
  s = reducer(s, { type: class="st">'INCREMENT', count: 10 })
  s = reducer(s, { type: class="st">'DECREMENT' })
  s = reducer(s, { type: class="st">'DECREMENT', count: 10 })
  s = reducer(s, { type: class="st">'SOME_OTHER_TYPE', someField: class="st">'value' })

  class="cm">// State shape is strictly checked.
  class="cm">// @ts-expect-error
  reducer(class="st">'string', { type: class="st">'INCREMENT' })

  class="cm">// Combined reducer also accepts any action.
  const combined = combineReducers({ sub: reducer })

  let cs: { sub: State } = combined(undefined, { type: class="st">'init' })
  cs = combined(cs, { type: class="st">'INCREMENT', count: 10 })

  class="cm">// Combined reducer's state is strictly checked.
  class="cm">// @ts-expect-error
  combined({ unknown: class="st">'' }, { type: class="st">'INCREMENT' })
}

/**
 * Reducer definition using discriminated unions.