**Course Title:** Mastering Vue.js: Building Modern Web Applications **Section Title:** Vue Router: Building SPAs **Topic:** Navigation guards for route protection **Introduction** As you build Single-Page Applications (SPAs) with Vue Router, you'll often need to restrict access to certain routes based on user authentication or other conditions. Navigation guards are a powerful tool in Vue Router that allow you to achieve this by intercepting route changes and determining whether the user has permission to access a particular route. **What are Navigation Guards?** Navigation guards are functions that run before or after a route change. They can be used to perform various actions, such as: 1. Authenticating users before allowing them to access a route. 2. Checking if a user has the necessary permissions to access a route. 3. Redirecting users to a different route based on certain conditions. 4. Canceling a route change if the user doesn't meet certain criteria. **Types of Navigation Guards** There are three types of navigation guards in Vue Router: 1. **Global Guards**: These are defined on the router instance and run for every route change. 2. **Per-Route Guards**: These are defined on a specific route and run only for that route. 3. **In-Component Guards**: These are defined inside a component and run only for that component. **Defining Navigation Guards** To define a navigation guard, you need to create a function that takes three parameters: * `to`: The route the user is going to. * `from`: The route the user is coming from. * `next`: A callback function that must be called to resolve the route change. Here is an example of a simple global guard that checks if a user is authenticated before allowing them to access a route: ```javascript const router = new VueRouter({ routes: [ { path: '/protected', component: ProtectedComponent, meta: { requiresAuth: true } } ] }) router.beforeEach((to, from, next) => { if (to.meta.requiresAuth && !auth.isLoggedIn) { next('/login') } else { next() } }) ``` **Per-Route Guards** You can also define guards on a per-route basis by adding a `beforeEnter` property to the route configuration: ```javascript const routes = [ { path: '/protected', component: ProtectedComponent, beforeEnter: (to, from, next) => { if (!auth.isLoggedIn) { next('/login') } else { next() } } } ] ``` **In-Component Guards** You can also define guards inside a component using the `beforeRouteEnter` and `beforeRouteUpdate` lifecycle hooks: ```javascript export default { beforeRouteEnter(to, from, next) { if (!auth.isLoggedIn) { next('/login') } else { next() } }, beforeRouteUpdate(to, from, next) { if (!auth.isLoggedIn) { next('/login') } else { next() } } } ``` **Conclusion** Navigation guards are a powerful feature of Vue Router that allow you to restrict access to certain routes based on user authentication or other conditions. By defining global, per-route, or in-component guards, you can ensure that your application is secure and that users can only access routes that they have permission to. **Practice Exercise** Try defining a global guard that checks if a user is authenticated before allowing them to access a route. Then, try defining a per-route guard that checks if a user has a specific permission before allowing them to access a route. **Leave a Comment** Have you used navigation guards in your Vue Router applications? What kind of guards have you defined and how have they helped you improve the security and functionality of your applications? **Additional Resources** For more information on Vue Router and navigation guards, you can visit the official Vue Router documentation: [https://router.vuejs.org/guide/advanced/navigation-guards.html](https://router.vuejs.org/guide/advanced/navigation-guards.html) **What's Next** In the next topic, we'll explore the concept of state management and how to use Vuex to manage the state of your Vue applications.