diff --git a/modules/ppcp-settings/resources/js/data/onboarding/reducer.js b/modules/ppcp-settings/resources/js/data/onboarding/reducer.js
index 5c1f59263..9cdeb7018 100644
--- a/modules/ppcp-settings/resources/js/data/onboarding/reducer.js
+++ b/modules/ppcp-settings/resources/js/data/onboarding/reducer.js
@@ -1,22 +1,13 @@
+import { createReducer, createSetters } from '../utils';
 import ACTION_TYPES from './action-types';
 
-const defaultState = {
+// Store structure.
+
+const defaultTransient = {
 	isReady: false,
 	isSaving: false,
 	isManualConnectionBusy: false,
 
-	// Data persisted to the server.
-	data: {
-		completed: false,
-		step: 0,
-		useSandbox: false,
-		useManualConnection: false,
-		clientId: '',
-		clientSecret: '',
-		isCasualSeller: null, // null value will uncheck both options in the UI.
-		products: [],
-	},
-
 	// Read only values, provided by the server.
 	flags: {
 		canUseCasualSelling: false,
@@ -25,29 +16,33 @@ const defaultState = {
 	},
 };
 
+const defaultPersistent = {
+	completed: false,
+	step: 0,
+	useSandbox: false,
+	useManualConnection: false,
+	clientId: '',
+	clientSecret: '',
+	isCasualSeller: null, // null value will uncheck both options in the UI.
+	products: [],
+};
+
+// Reducer logic.
+
+const [ setTransient, setPersistent ] = createSetters(
+	defaultTransient,
+	defaultPersistent
+);
+
+const defaultState = {
+	...defaultTransient,
+	data: { ...defaultPersistent },
+};
+
 export const onboardingReducer = (
 	state = defaultState,
 	{ type, ...action }
 ) => {
-	const setTransient = ( changes ) => {
-		const { data, ...transientChanges } = changes;
-		return { ...state, ...transientChanges };
-	};
-
-	const setPersistent = ( changes ) => {
-		const validChanges = Object.keys( changes ).reduce( ( acc, key ) => {
-			if ( key in defaultState.data ) {
-				acc[ key ] = changes[ key ];
-			}
-			return acc;
-		}, {} );
-
-		return {
-			...state,
-			data: { ...state.data, ...validChanges },
-		};
-	};
-
 	switch ( type ) {
 		// Reset store to initial state.
 		case ACTION_TYPES.RESET_ONBOARDING:
diff --git a/modules/ppcp-settings/resources/js/data/utils.js b/modules/ppcp-settings/resources/js/data/utils.js
new file mode 100644
index 000000000..2cec07815
--- /dev/null
+++ b/modules/ppcp-settings/resources/js/data/utils.js
@@ -0,0 +1,75 @@
+/**
+ * Updates an object with new values, filtering based on allowed keys.
+ *
+ * Helper method used by createSetters.
+ *
+ * @param {Object} oldObject   The original object to update.
+ * @param {Object} newValues   The new values to apply.
+ * @param {Object} allowedKeys An object whose keys define the allowed keys to update.
+ * @return {Object} A new object with the allowed updates applied.
+ */
+const updateObject = ( oldObject, newValues, allowedKeys = {} ) => ( {
+	...oldObject,
+	...Object.keys( newValues ).reduce( ( acc, key ) => {
+		if ( key in allowedKeys ) {
+			acc[ key ] = newValues[ key ];
+		}
+		return acc;
+	}, {} ),
+} );
+
+/**
+ * Creates setter functions for updating state.
+ *
+ * Only properties that are present in the "defaultTransient" or "defaultPersistent"
+ * arguments can be updated by the setters. Make sure that the default state defines
+ * ALL possible properties.
+ *
+ * @param {Object} defaultTransient  Object defining initial transient values.
+ * @param {Object} defaultPersistent Object defining initial persistent values.
+ * @return {[Function, Function]} An array containing setTransient and setPersistent functions.
+ */
+export const createSetters = ( defaultTransient, defaultPersistent ) => {
+	const setTransient = ( oldState, newValues ) =>
+		updateObject( oldState, newValues, defaultTransient );
+
+	const setPersistent = ( oldState, newValues ) => ( {
+		...oldState,
+		data: updateObject( oldState.data, newValues, defaultPersistent ),
+	} );
+
+	return [ setTransient, setPersistent ];
+};
+
+/**
+ * Creates a reducer function with predefined action handlers.
+ *
+ * @param {Object} defaultTransient  Object defining initial transient values.
+ * @param {Object} defaultPersistent Object defining initial persistent values.
+ * @param {Object} handlers          An object mapping action types to handler functions.
+ * @return {Function} A reducer function.
+ */
+export const createReducer = (
+	defaultTransient,
+	defaultPersistent,
+	handlers
+) => {
+	if ( Object.hasOwnProperty.call( defaultTransient, 'data' ) ) {
+		throw new Error(
+			'The transient state cannot contain a "data" property.'
+		);
+	}
+
+	const initialState = {
+		...defaultTransient,
+		data: defaultPersistent,
+	};
+
+	return function reducer( state = initialState, action ) {
+		if ( Object.hasOwnProperty.call( handlers, action.type ) ) {
+			return handlers[ action.type ]( state, action.data );
+		}
+
+		return state;
+	};
+};