unstable_batchedUpdates

Implements batchedUpdates and exposes as unstable_batchedUpdates. All
nested synchronous updates are automatically batched.

src/renderers/dom/fiber/ReactDOMFiber.js

@@ -165,6 +165,10 @@ var ReactDOM = {
     return DOMRenderer.findHostInstance(component);
   },
 
+  unstable_batchedUpdates(fn : Function) : void {
+    DOMRenderer.batchedUpdates(fn);
+  },
+
 };
 
 module.exports = ReactDOM;

src/renderers/shared/fiber/ReactFiberReconciler.js

@@ -68,6 +68,7 @@ export type Reconciler<C, I, TI> = {
   updateContainer(element : ReactElement<any>, container : OpaqueNode) : void,
   unmountContainer(container : OpaqueNode) : void,
   performWithPriority(priorityLevel : PriorityLevel, fn : Function) : void,
+  batchedUpdates(fn: Function) : void,
 
   // Used to extract the return value from the initial render. Legacy API.
   getPublicRootInstance(container : OpaqueNode) : (ReactComponent<any, any, any> | TI | I | null),
@@ -78,7 +79,11 @@ export type Reconciler<C, I, TI> = {
 
 module.exports = function<T, P, I, TI, C>(config : HostConfig<T, P, I, TI, C>) : Reconciler<C, I, TI> {
 
-  var { scheduleWork, performWithPriority } = ReactFiberScheduler(config);
+  var {
+    scheduleWork,
+    performWithPriority,
+    batchedUpdates,
+  } = ReactFiberScheduler(config);
 
   return {
 
@@ -142,6 +147,8 @@ module.exports = function<T, P, I, TI, C>(config : HostConfig<T, P, I, TI, C>) :
 
     performWithPriority,
 
+    batchedUpdates,
+
     getPublicRootInstance(container : OpaqueNode) : (ReactComponent<any, any, any> | I | TI | null) {
       const root : FiberRoot = (container.stateNode : any);
       const containerFiber = root.current;

src/renderers/shared/fiber/ReactFiberScheduler.js

@@ -508,12 +508,10 @@ module.exports = function<T, P, I, TI, C>(config : HostConfig<T, P, I, TI, C>) {
   }
 
   function performSynchronousWork() {
-    if (useSyncScheduling) {
-      // Start batching updates
-      shouldBatchUpdates = true;
-    }
-    performAndHandleErrors(performSynchronousWorkUnsafe);
-    shouldBatchUpdates = false;
+    // All nested updates are batched
+    batchedUpdates(() => {
+      performAndHandleErrors(performSynchronousWorkUnsafe);
+    });
   }
 
   function scheduleSynchronousWork(root : FiberRoot) {
@@ -534,6 +532,7 @@ module.exports = function<T, P, I, TI, C>(config : HostConfig<T, P, I, TI, C>) {
       lastScheduledRoot = root;
 
       if (!shouldBatchUpdates) {
+        // Unless in batched mode, perform work immediately
         performSynchronousWork();
       }
     }
@@ -690,9 +689,20 @@ module.exports = function<T, P, I, TI, C>(config : HostConfig<T, P, I, TI, C>) {
     }
   }
 
+  function batchedUpdates(fn: Function) {
+    const prev = shouldBatchUpdates;
+    shouldBatchUpdates = true;
+    try {
+      fn();
+    } finally {
+      shouldBatchUpdates = prev;
+    }
+  }
+
   return {
     scheduleWork: scheduleWork,
     scheduleDeferredWork: scheduleDeferredWork,
     performWithPriority: performWithPriority,
+    batchedUpdates: batchedUpdates,
   };
 };