This article will take you through something that must be asked in the interview---the navigation hook in Vue-Router. I hope it will be helpful to you!

Navigation Guard

"Navigation" indicates that the route is changing.

vue-router The navigation guards provided are mainly used to guard navigation by jumping or canceling. There are multiple opportunities to build into the route navigation process: globally, exclusive to a single route, or at the component level. [Related recommendations: "vue.js Tutorial"]

1. Global front guard----router.beforeEach

router.beforeEach Register a global front guard:

const router = new VueRouter({ ... })

router.beforeEach((to, from, next) => {
  //  to:要去哪个页面
  //  from:从哪里来
  //  next:它是一个函数。
  //     如果直接放行 next()
  //     如果要跳到其它页 next(其它页)
})

Sample code:

router.beforeEach(async(to, from, next) => {
  NProgress.start() // 开启进度条
  const token = store.state.user.token
  const userId = store.state.user.userInfo.userId
  console.log(token, to.path, from.path)
  if (token) {
    if (to.path === '/login') { // 有 token还要去login
      next('/')
      NProgress.done() // 关闭进度条
    } else { // 有 token，去其他页面，放行
      if (!userId) {
        await store.dispatch('user/getUserInfo')
      }
      next()
    }
  } else {
    if (to.path === '/login') { // 没有token，去login，放行
      next()
    } else {
      next('/login') // 没有token，去其他页面
      NProgress.done()
    }
  }
})

Summary

• router.beforeEach (callback (three parameters))
• In the navigation guard function, be sure to call next()
• to.path: to is a routing object, path represents the path and is one of its attributes

2. Global post hook----router.afterEach

router.afterEach Register a global post-hook:

You can also register a global post-hook, but unlike guards, these hooks will not accept next The function will not change the navigation itself:

router.afterEach((to, from) => {
  // ...
})

3. Global resolution guard----router.beforeResolve

In 2.5.0 you can Use router.beforeResolve to register a global guard. This is similar to router.beforeEach, the difference is that before the navigation is confirmed, the guard is in all components at the same time and after the asynchronous routing component is parsed , the parsing guard is called.

4. Route-exclusive guards

You can define it directly in the routing configuration beforeEnter Guard:

const router = new VueRouter({
  routes: [
    {
      path: '/foo',
      component: Foo,
      beforeEnter: (to, from, next) => {
        // ...
      }
    }
  ]
})

5. Guards within the component

• beforeRouteEnter
• ##beforeRouteUpdate (New in 2.2)
• beforeRouteLeave

const Foo = {
  template: `...`,
  beforeRouteEnter(to, from, next) {
    // 在渲染该组件的对应路由被 confirm 前调用
    // 不！能！获取组件实例 `this`
    // 因为当守卫执行前，组件实例还没被创建
  },
  beforeRouteUpdate(to, from, next) {
    // 在当前路由改变，但是该组件被复用时调用
    // 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`
  }
}

Copy after login

Complete navigation parsing process

• Navigation is triggered.

• Call the

  beforeRouteLeave guard in the deactivated component.

• Call the global

  beforeEach guard.

• Call

  beforeRouteUpdate guards (2.2) in reused components.

• Call

  beforeEnter in the routing configuration.

• Resolve asynchronous routing components.

• Call

  beforeRouteEnter in the activated component.

• Call the global

  beforeResolve guard (2.5).

• Navigation confirmed.

• Call the global

  afterEach hook.

• Trigger DOM update.

• Call the callback function passed to

  next in the beforeRouteEnter guard, and the created component instance will be passed in as a parameter of the callback function.

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