Promise based filter function

package.json

@@ -26,6 +26,7 @@
     "build": "rollup -c build/rollup.config.js",
     "prepublishOnly": "npm run build",
     "pretest": "npm run build",
+    "prepare": "npm run build",
     "test": "cd test && mocha -r ts-node/register *.ts",
     "test:dirty": "cd test && mocha -r ts-node/register *.ts",
     "cover": "nyc npm test"

src/PersistOptions.ts

@@ -44,7 +44,7 @@ export interface PersistOptions<S> {
    * Check mutations using <code>mutation.type</code>
    * @param mutation object of type {@link Payload}
    */
-  filter?: (mutation: Payload) => boolean
+  filter?: (mutation: Payload) => Promise<boolean> | boolean
 
   /**
    * Names of modules that you want to persist.

src/index.ts

@@ -21,7 +21,7 @@ export class VuexPersistence<S> implements PersistOptions<S> {
   public saveState: (key: string, state: {}, storage?: AsyncStorage | Storage) => Promise<void> | void
   public reducer: (state: S) => Partial<S>
   public key: string
-  public filter: (mutation: Payload) => boolean
+  public filter: (mutation: Payload) => Promise<boolean> | boolean
   public modules: string[]
   public strictMode: boolean
   public supportCircular: boolean
@@ -237,7 +237,15 @@ export class VuexPersistence<S> implements PersistOptions<S> {
         }
 
         this.subscriber(store)((mutation: MutationPayload, state: S) => {
-          if (this.filter(mutation)) {
+          const result = this.filter(mutation)
+          const promise = result as Promise<boolean>
+          if (promise.then) {
+            promise.then((val) => {
+              if (val) {
+                this.saveState(this.key, this.reducer(state), this.storage)
+              }
+            })
+          } else if (this.filter(mutation)) {
             this.saveState(this.key, this.reducer(state), this.storage)
           }
         })

test/vuex-defaultstorage-asyncfilter.spec.ts

@@ -0,0 +1,51 @@
+/**
+ * Created by championswimmer on 23/07/17.
+ */
+
+import { assert, expect, should } from 'chai'
+import Vue from 'vue'
+import { Store } from 'vuex'
+import Vuex from 'vuex'
+import VuexPersistence from '..'
+
+Vue.use(Vuex)
+const vuexPersist = new VuexPersistence()
+vuexPersist.filter = async (mutation) => (mutation.type === 'dogBark')
+console.log((vuexPersist.storage as Storage).getItem('vuex') as string)
+const store = new Store<any>({
+  state: {
+    dog: {
+      barks: 0
+    },
+    cat: {
+      mews: 0
+    }
+  },
+  mutations: {
+    dogBark(state) {
+      state.dog.barks++
+    },
+    catMew(state) {
+      state.cat.mews++
+    }
+  },
+  plugins: [vuexPersist.plugin]
+})
+const getSavedStore = () => JSON.parse((vuexPersist.storage as Storage).getItem('vuex') as string)
+
+describe('Storage: Default Storage, Test: reducer, async-filter; Strict Mode: OFF', () => {
+  it('should persist reduced state', async () => {
+    store.commit('dogBark')
+    await ptimeout() // wait for store.commit
+    expect(getSavedStore().dog.barks).to.equal(1)
+    store.commit('catMew')
+    //noinspection TsLint
+    expect(getSavedStore().cat.mews).to.equal(0)
+  })
+})
+
+function ptimeout(ms = 10) {
+  return new Promise((resolve, reject) => {
+    setTimeout(() => resolve(), ms)
+  })
+}