# Step 2.5: Redux: Reducers (Exercise)

[Lessons](../) | [Exercise](./exercise/) | [Demo](./demo/)

If you still have the app running from a previous step, stop it with `ctrl+c`. Start the tests instead by running `npm test` from the root of the `frontend-bootcamp` folder.

1. First, take a look at the store interface in `exercise/src/store/index.ts`. Note that the `Store` interface has two keys: `todos` and `filter`. We'll concentrate on `todos`, which is an object where the keys are string IDs and the values are of a `TodoItem` type.

2. Open `exercise/src/reducers/index.ts` and fill in the missing case statements for the switch on `action.type`.

3. Open `exercise/src/index.tsx` and write separate dispatch calls.

4. Take a look what is written in the console (F12 on PC, cmd-option-I on Mac).

5. Install the [Chrome](https://chrome.google.com/webstore/detail/redux-devtools/lmhkpmbekcpmknklioeibfkpmmfibljd) or [Firefox](https://addons.mozilla.org/en-US/firefox/addon/reduxdevtools/) extensions

6. Observe the state changes, try doing "time travel"