Learning Redux

Defining the undoable higher-order reducer

Our goal is to create a generic undo/redo higher-order reducer, which we will call undoable (because it makes a reducer function undoable):

1. Create a new file src/undoable.js.
2. We start with the function definition. It is a higher-order function that takes a reducer function as an argument:

export default function undoable (reducer) {

3. Then, we need to return a new reducer function, which means we will need to think of the initial state of our higher-order reducer. For now, let's define a constant initialState and set it to {}:

  const initialState = {} // TODO

4. Now, we can return the (to-be enhanced) reducer function:

  return function enhancedReducer (state = initialState, action) {    // TODO  }