solution

src/transformState.js

@@ -4,20 +4,42 @@
  * @param {Object} state
  * @param {Object[]} actions
  */
+function addProperties(state, addObject) {
+  for (const addProperty in addObject) {
+    state[addProperty] = addObject[addProperty];
+  }
+}
+
+function removeProperties(state, arrProperties) {
+  for (const removeProperty of arrProperties) {
+    delete state[removeProperty];
+  }
+}
+
+function removeAllProperty(state) {
+  for (const key in state) {
+    delete state[key];
+  }
+}
+
 function transformState(state, actions) {
-  for (const action of actions) {
-    if (action.type === 'addProperties') {
-      for (const addProperty in action.extraData) {
-        state[addProperty] = action.extraData[addProperty];
+  for (const item of actions) {
+    switch (item.type) {
+      case 'addProperties': {
+        addProperties(state, item.extraData);
+        break;
       }
-    } else if (action.type === 'removeProperties') {
-      for (const removeProperty of action.keysToRemove) {
-        delete state[removeProperty];
+
+      case 'removeProperties': {
+        removeProperties(state, item.keysToRemove);
+        break;
       }
-    } else if (action.type === 'clear') {
-      for (const key in state) {
-        delete state[key];
+
+      case 'clear': {
+        removeAllProperty(state);
+        break;
       }
+      default: throw new Error('object does not know this type');
     }
   }