docs for beforeRouteUpdate

Author: yyx990803

docs/en/advanced/navigation-guards.md

@@ -64,7 +64,11 @@ These guards have the exact same signature as global before guards.
 
 ### In-Component Guards
 
-Finally, you can directly define route navigation guards inside route components (the ones passed to the router configuration) with `beforeRouteEnter` and `beforeRouteLeave`:
+Finally, you can directly define route navigation guards inside route components (the ones passed to the router configuration) with the following options:
+
+- `beforeRouteEnter`
+- `beforeRouteUpdate` (added in 2.2)
+- `beforeRouteLeave`
 
 ``` js
 const Foo = {
@@ -74,6 +78,14 @@ const Foo = {
     // does NOT have access to `this` component instance,
     // because it has not been created yet when this guard is called!
   },
+  beforeRouteUpdate (to, from, next) {
+    // called when the route that renders this component has changed,
+    // but this component is reused in the new route.
+    // For example, for a route with dynamic params /foo/:id, when we
+    // navigate between /foo/1 and /foo/2, the same Foo component instance
+    // will be reused, and this hook will be called when that happens.
+    // has access to `this` component instance.
+  },
   beforeRouteLeave (to, from, next) {
     // called when the route that renders this component is about to
     // be navigated away from.

docs/zh-cn/advanced/navigation-guards.md

@@ -65,7 +65,11 @@ const router = new VueRouter({
 
 ### 组件内的钩子
 
-最后，你可以使用 `beforeRouteEnter` 和 `beforeRouteLeave`，在路由组件内直接定义路由导航钩子，
+最后，你可以在路由组件内直接定义以下路由导航钩子：
+
+- `beforeRouteEnter`
+- `beforeRouteUpdate` (2.2 新增)
+- `beforeRouteLeave`
 
 ``` js
 const Foo = {
@@ -75,6 +79,12 @@ const Foo = {
     // 不！能！获取组件实例 `this`
     // 因为当钩子执行前，组件实例还没被创建
   },
+  beforeRouteUpdate (to, from, next) {
+    // 在当前路由改变，但是改组件被复用时调用
+    // 举例来说，对于一个带有动态参数的路径 /foo/:id，在 /foo/1 和 /foo/2 之间跳转的时候，
+    // 由于会渲染同样的 Foo 组件，因此组件实例会被复用。而这个钩子就会在这个情况下被调用。
+    // 可以访问组件实例 `this`
+  },
   beforeRouteLeave (to, from, next) {
     // 导航离开该组件的对应路由时调用
     // 可以访问组件实例 `this`