Add configurable handler to onWriteFail

docs/api.md

@@ -63,9 +63,13 @@ The Persistor is a redux store unto itself, plus
   debug?: boolean, // true -> verbose logs
   stateReconciler?: false | StateReconciler, // false -> do not automatically reconcile state
   serialize?: boolean, // false -> do not call JSON.parse & stringify when setting & getting from storage
+  writeFailHandler?: Function, // will be called if the storage engine fails during setItem()
 }
 ```
 
+Persisting state involves calling setItem() on the storage engine. By default, this will fail silently if the storage/quota is exhausted.  
+Provide a writeFailHandler(error) function to be notified if this occurs.
+
 ### `type MigrationManifest`
 ```js
 {

src/createPersistoid.js

@@ -17,6 +17,7 @@ export default function createPersistoid(config: PersistConfig): Persistoid {
   }${config.key}`
   const storage = config.storage
   const serialize = config.serialize === false ? x => x : defaultSerialize
+  const writeFailHandler = config.writeFailHandler || null
 
   // initialize stateful values
   let lastState = {}
@@ -107,6 +108,7 @@ export default function createPersistoid(config: PersistConfig): Persistoid {
 
   function onWriteFail(err) {
     // @TODO add fail handlers (typically storage full)
+    if (writeFailHandler) writeFailHandler(err)
     if (err && process.env.NODE_ENV !== 'production') {
       console.error('Error storing data', err)
     }

src/types.js

@@ -25,6 +25,7 @@ export type PersistConfig = {
   debug?: boolean,
   serialize?: boolean,
   timeout?: number,
+  writeFailHandler?: Function,
 }
 
 export type PersistorOptions = {