Add transaction capability to asyncActions

for relating pending/success/failure actions. Particularly useful for mapping
a failure to a pending action to roll back any optimistic updates.

src/actions/actionCreators.js

@@ -31,18 +31,30 @@ limitations under the License.
  *                         `${id}.pending` and either
  *                         `${id}.success` or
  *                         `${id}.failure`.
+ *
+ *                     The shape of each are:
+ *                     { action: '${id}.pending', request, asyncId }
+ *                     { action: '${id}.success', result, asyncId }
+ *                     { action: '${id}.failure', err, asyncId }
+ *
+ *                     where `request` is returned by `pendingFn`, result
+ *                     is the result of the promise returned by `fn` and
+ *                     `asyncId` is a unique ID for each dispatch of the
+ *                     asynchronous action.
  */
 export function asyncAction(id, fn, pendingFn) {
     return (dispatch) => {
+        const asyncId = Math.random().toString(16).slice(2, 10);
         dispatch({
             action: id + '.pending',
             request:
                 typeof pendingFn === 'function' ? pendingFn() : undefined,
+            asyncId,
         });
         fn().then((result) => {
-            dispatch({action: id + '.success', result});
+            dispatch({action: id + '.success', result, asyncId});
         }).catch((err) => {
-            dispatch({action: id + '.failure', err});
+            dispatch({action: id + '.failure', err, asyncId});
         });
     };
 }