1 files changed, 27 insertions, 0 deletions
diff --git a/packages/gitbook-core/src/lib/createReducer.js b/packages/gitbook-core/src/lib/createReducer.js
new file mode 100644
index 0000000..2ebecfb
--- /dev/null
+++ b/packages/gitbook-core/src/lib/createReducer.js
@@ -0,0 +1,27 @@
+
+/**
+ * Helper to create a reducer that extend the store.
+ *
+ * @param  {String} property
+ * @param  {Function(state, action): state} reduce
+ * @return {Function(state, action): state}
+ */
+function createReducer(name, reduce) {
+    return (state, action) => {
+        const value = state[name];
+        const newValue = reduce(value, action);
+
+        if (newValue === value) {
+            return state;
+        }
+
+        const newState = {
+            ...state,
+            [name]: newValue
+        };
+
+        return newState;
+    };
+}
+
+module.exports = createReducer;