[new feature] Tab: add scroll event (#1730)

packages/tab/demo/index.vue

@@ -9,7 +9,7 @@
     </demo-block>
 
     <demo-block :title="$t('title2')">
-      <van-tabs>
+      <van-tabs sticky @scroll="subscribeSticky">
         <van-tab v-for="index in 8" :title="$t('tab') + index" :key="index">
           {{ $t('content') }} {{ index }}
         </van-tab>
@@ -111,6 +111,10 @@ export default {
 
     onClick(index, title) {
       this.$toast(title);
+    },
+
+    subscribeSticky(e) {
+      console.log(e);
     }
   }
 };
@@ -137,9 +141,11 @@ export default {
   .custom-tabwrap .van-tab-active {
     color: #20a0ff;
   }
+
   .custom-tabwrap .van-tabs-nav-bar {
     background: #20a0ff;
   }
+
   .custom-pane {
     text-align: center;
     height: 50px;

packages/tab/en-US.md

@@ -169,3 +169,4 @@ In swipeable mode, you can switch tabs with swipe gestrue in the content
 | click | Triggered when click tab | index：index of current tab，title: tab title |
 | change | Triggered when active tab changed | index：index of current tab，title: tab title |
 | disabled | Triggered when click disabled tab | index：index of current tab, title: tab title |
+| scroll | Triggered when tab scroll | e：scroll arguments |

packages/tab/zh-CN.md

@@ -171,3 +171,4 @@ export default {
 | click | 点击标签时触发 | index：标签索引，title：标题 |
 | change | 当前激活的标签改变时触发 | index：标签索引，title：标题 |
 | disabled | 点击被禁用的标签时触发 | index：标签索引，title：标题 |
+| scroll | 滚动时触发 | e：滚动参数 |

packages/tabs/index.vue

@@ -231,6 +231,11 @@ export default create({
       } else {
         this.position = '';
       }
+      const scrollParams = {
+        scrollTop,
+        isFixed: this.position === 'top'
+      };
+      this.$emit('scroll', scrollParams);
     },
 
     // update nav bar style