feat(Stepper): add new prop async-change @rex-zsd (#2318)

packages/stepper/demo/index.vue

@@ -11,9 +11,18 @@
       />
     </demo-block>
 
+    <demo-block :title="$t('asyncChange')">
+      <van-stepper
+        :value="stepper2"
+        integer
+        async-change
+        @change="onChange"
+      />
+    </demo-block>
+
     <demo-block :title="$t('advancedUsage')">
       <van-stepper
-        v-model="stepper2"
+        v-model="stepper3"
         integer
         :min="5"
         :max="40"
@@ -26,11 +35,26 @@
 
 <script>
 export default {
+  i18n: {
+    'zh-CN': {
+      asyncChange: '异步变更'
+    },
+    'en-US': {
+      asyncChange: 'Async Change',
+    }
+  },
+
   data() {
     return {
       stepper1: 1,
-      stepper2: null
+      stepper2: 10,
+      stepper3: null
     };
+  },
+  methods: {
+    onChange(event) {
+      this.$toast(`change: ${event}`);
+    }
   }
 };
 </script>