Commented solution using switch statement (#35623)

* Commented solution using switch statement

* fix: used two-space indentation

guide/english/certifications/front-end-libraries/react-and-redux/extract-state-logic-to-redux/index.md

@@ -3,35 +3,34 @@ title: Extract State Logic to Redux
 ---
 ## Extract State Logic to Redux
 
-This is a stub. <a href='https://github.com/freecodecamp/guides/tree/master/src/pages/certifications/front-end-libraries/react-and-redux/extract-state-logic-to-redux/index.md' target='_blank' rel='nofollow'>Help our community expand it</a>.
-
-<a href='https://github.com/freecodecamp/guides/blob/master/README.md' target='_blank' rel='nofollow'>This quick style guide will help ensure your pull request gets accepted</a>.
-
-<!-- The article goes here, in GitHub-flavored Markdown. Feel free to add YouTube videos, images, and CodePen/JSBin embeds  -->
-
-Suggested solution: 
 
+### Solution
 ```javascript
+// define ADD, addMessage(), messageReducer(), and store here:
 const ADD = 'ADD';
-
-function addMessage(message) {
-  return {
+const addMessage = (message) => {
+  return ({
     type: ADD,
-    message: message
-  };
-};
-
-function messageReducer (previousState, action) {
-  return [...previousState, action.message];
+    message
+  })
 }
 
-let store = {
-  state: [],
-  getState: () => store.state,
-  dispatch: (action) => {
-    if (action.type === ADD) {
-      store.state = messageReducer(store.state, action);
-    }
+// Use ES6 default paramter to give the 'previousState' parameter an initial value.
+const messageReducer = (previousState = [], action) => {
+
+  // Use switch statement to lay out the reducer logic in response to different action type
+  switch (action.type) {
+    case ADD:
+
+      // Use ES6 spread operator to return a new array where the new message is added to previousState
+      return [...previousState, action.message]
+      break;
+
+    default:
+      // A default case to fall back on in case if the update to Redux store is not for this specific state.
+      return previousState;
   }
-};
+}
+
+const store = Redux.createStore(messageReducer);
 ```