Why do you need to call Vue.use(VueRouter) in the index.js file under the router folder?

The necessity of Vue Router registration in index.js

In Vue projects, especially in the index.js file under router folder, you often see the line of Vue.use(VueRouter) which raises questions about its necessity. The purpose of this line of code is to register the Vue Router plug-in to the Vue instance, but its necessity is closely related to the Vue version.

Global registration for Vue 2:

In Vue 2, Vue.use(VueRouter) is a global registration that injects the functionality of Vue Router into all Vue instances. This means that no matter how many Vue instances you create, they can directly access and use the routing functionality. This is because the plug-in system of Vue 2 is designed to be global. The code structure is usually as follows:

 import Vue from 'vue';
import VueRouter from 'vue-router';

Vue.use(VueRouter);

const router = new VueRouter({ /* ...routing configuration */ });

export default router;

In main.js , you just need:

 new Vue({
  router,
  // ...Other configuration});

Local registration for Vue 3:

Vue 3 uses a different approach. createApp() creates an application instance, use() method is applied to this specific instance. This means that the functionality of Vue Router is only valid for this application instance. The code structure is usually as follows:

 import { createRouter, createWebHistory } from 'vue-router';
import { createApp } from 'vue';

const router = createRouter({
  history: createWebHistory(),
  routes: [ /* ...Routing configuration */ ],
});

const app = createApp(/* ... */);
app.use(router);
app.mount('#app');

The role of Vue.use(VueRouter) in index.js :

In Vue 2 projects, Vue.use(VueRouter) in index.js is necessary because it is responsible for global registration of Vue Router. Without this line of code, the Vue instance will not be able to access the routing function. However, in Vue 3 projects, this line of code is usually unnecessary in index.js , because the registration of the route is done in main.js or in the entry file via app.use(router) .

Summarize:

The necessity of Vue.use(VueRouter) in index.js depends on your Vue version. In Vue 2, it is a necessary step for global registration; in Vue 3, it is usually redundant because Vue 3 uses an application instance-based registration method. Understanding this difference helps to better understand how Vue Router is used and the differences between Vue 2 and Vue 3.

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