State Reducer, solution

Add a state reducer option to the useToggle hook

This lesson is part of the epicreact.dev’s Advanced React Patterns module

OK! Let’s invert control of our useToggle hook. We only need to make one major change to our implementation. So,

• Open the toggle, module.
• In the useToggle hook, take reducer as an option.
• And replace all local toggleReducer calls with the optional reducer.

export function useToggle({initialOn = false, reducer} = {}) {
  const {current: initialState} = React.useRef<ToggleState>({
    on: initialOn,
  })
  const [state, dispatch] = React.useReducer(
    toggleReducerreducer,
    initialState
  )
  /* ...rest of implementation... */
}

Unfortunately, requiring a reducer function (as an argument) has the undesirable effect of breaking it everywhere that a reducer isn’t defined.

Assign a default state reducer to retain existing behavior

We can retain the previous experience with a default value assignment syntax.

• Add toggleReducer as the default assignment for reducer
  • This is used only if the value is undefined.
• Note: that this resolves our TypeScript errors and the UI continues to works as it did before.

export function useToggle({
  initialOn = false,
  reducer = toggleReducer,
} = {}) {
  /* ...rest of implementation... */
}

Provide a custom state reducer at the the call site

Now we can override the default toggleReducer — by providing a reducer option. Let’s provide a state reducer function that dispables the toggle when we’ve hit our click limit.

• For now, copy the toggleReducer declaration and paste it into the app module — passing it in as reducer.
• (Don’t worry, we’ll come back to fix the types after we get it working)

const {on, getTogglerProps, getResetterProps} = useToggle({
  reducer(state: ToggleState, action: ToggleAction) {
    switch (action.type) {
      case 'toggle': {
        return {on: !state.on}
      }
      case 'reset': {
        return action.initialState
      }
    }
  },
})

With our override state reducer in place, add the additional toggle logic.

• For the toggle action, add a condition
• If clickedTooMuch is truthy, return the current (unmodified) state.

const {on, getTogglerProps, getResetterProps} = useToggle({
  reducer: function toggleReducer(
    state: ToggleState,
    action: ToggleAction
  ) {
    switch (action.type) {
      case 'toggle': {
        if (clickedTooMuch) {
          return state
        }
        return {on: !state.on}
      }
      case 'reset': {
        return action.initialState
      }
    }
  },
})

What we did

We’ve made it possible to override the default behavior of our useToggle hook, at the call site. This lets others extend the hook’s capabilities without having to modify the original code!

And by using the keeping the previous implementation as default, we’ve protecting exitisting code from a breaking change.

Resolving the TypeScript errors

All that’s left is to fix the TypeScript errors.

[Marker: TypeScript]

• Open the toggle module.
• Export the two type definitions that we now need access to in the app module.
• Go back to the app module.
• In VS Code,
  • Hover the error.
  • And select Quick Fix (or type ⌘.).
• We can select Update import from "./toggle" for each import. Or Add all missing imports and add them all in one go.
• If using a different editor, manually add the types to the toggle module statement.

import {
  ToggleAction,
  ToggleState,
  useToggle,
} from './toggle.tsx'
/* ...rest of implementation... */