Vue+beforeEnter uses hook function-JS Tutorial-php.cn

Vue+beforeEnter uses hook function

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Release： 2018-04-27 09:37:15

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This time I will bring you the hook function of Vue beforeEnter. What are the precautions for using the hook function of Vue beforeEnter? The following is a practical case, let's take a look.

Why do we need to create our own beforeEnter hook function?

Look at the problem scenario: There is a word list page in the project. Each cell will note whether the word has been mastered. Click on the cell to enter the details page, where you can learn the word and mark it. Whether the word is mastered, and you can also learn other words by clicking the forward and back buttons on the details page. So when I click return, the word list should show the latest status of all word users.

The final page relationship is like this:

wordListPage ——> wordDetail (learn a series of words, exit) ——> wordListPage (refresh words List)

For the above scenario, it is not possible to use the Vue

life cycle function, because Vue’s life cycle functions such as: beforeCreate, created, beforeMounted, mounted, etc., can only be used when the component is initialized. It will be called only when the component (VM instance) comes from the cache (such as $route.go(-1), keep-alive), the life cycle function will no longer be called. Therefore, when I return to the list page from the word details page, I cannot find a suitable period to start the dataupdate. Therefore, the above scenario cannot be handled well.

Of course, the above scenarios are relatively rare, but the existence of the beforeEnter hook function is still necessary.

Construct the beforeEnter hook function

Dependent knowledge points:

Routing: vue-router
Mixin: mixin
Central
EventBus

1. Create a central event bus

For the central event bus, a simple understanding is to create a public Vue instance (EventBus) and use the same instance in different places to trigger EventBus.$emit('demo' ) message, use a public Vue instance to listen to EventBus.$on('demo',() => {}) where you want to listen to the event. To put it bluntly, there is such a public component that sends messages to different places and listens for messages in different places. So the sending and receiving of messages is implemented by itself, so we call it the central event bus.

The code is as follows: libs/EventBus.js

import Vue from 'vue';
const EventBus = new Vue();
export default EventBus;

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Let’s see how to use it

2. Routing hook function beforeEach

Through the beforeEach hook function, the beforeEnter event of the corresponding component is triggered when the route is switched.

The code is as follows: router/index.js

import EventBus from '@/libs/EventBus';
router.beforeEach((to, from, next) => {
  //如：EventBus.$emit('homeBeforeEnter');
  EventBus.$emit(to.name + 'BeforeEnter'); 
  if (to.matched.some(route => route.meta.isAuth)) {
    ...
    next()
  } else {
    next()
  }
})

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3. Create a global mix-in object

Here to implement the monitoring of route switching events and component instance hooks Triggering of function beforeEnter.

libs/beforeEnterMixin.js

import EventBus from './EventBus';
export default {
  beforeCreate() {
    //获取当前路由名称，与前面使用to.name对应
    let vmName = this.$route.name;
    if (!vmName) {
      return;
    }
    // 当组件初始化时，先触发一次，后续将不再调用
    this.$options.beforeEnter();
    const beforeEnter = vmName + 'BeforeEnter';
    //监听路由切换时触发的...BeforeEnter事件
    //通过this.$options获取到实例中的beforeEnter钩子函数
    //监听到...BeforeEnter事件后，触发钩子函数beforeEnter调用
    EventBus.$on(beforeEnter, this.$options.beforeEnter);
  },
  //该函数在这里只作为占位，没有实际意义
  beforeEnter() {}
};

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For this mixin object, it is feasible to use global or local mixin.

Global mixing: main.js

import beforeEnterMixin from '@/libs/beforeEnterMixin';
Vue.mixin(beforeEnterMixin);

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4. Use in components

For example: home.vue

<template>
  <p>
    首页
  </p>
</template>
<script>
export default {
  beforeEnter() {
    console.log('首页 beforeEnter...');
  },
  created() {
    console.log('首页 created...')
  }
}
</script>

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At this point, our beforeEnter is complete. You can make a demo to test it yourself. Currently, I use it in many projects.

I believe you have mastered the method after reading the case in this article. For more exciting information, please pay attention to other related articles on the php Chinese website!