With Vue Router you might want to guard som paths and redirect users to a signup page if they are not authenticated. I will show you how this is done correctly with Firebase Authentication.

This article assumes you already have implemented your project with Vue Router and Firebase Authentication

First, we must mark each route that we want to guard with a meta property called requiresAuth.

const routes = [
  {
    path: '/signin',
    name: 'signin',
    component: () => import('../views/SignIn.vue')
  },
  {
    path: '/profile',
    name: 'profile',
    component: () => import('../views/Profile.vue'),
    meta: {
      requiresAuth: true
    }
  }
]

In this example, the path /signin is allowed for everyone, but /profile should only be for signed-in users.

Now we can use the beforeEach guard to check for this property.

router.beforeEach(async (to, from, next) => {
  const requiresAuth = to.matched.some(record => record.meta.requiresAuth);
  if (requiresAuth && !currentUser){
    next('signin');
  }else{
    next();
  }
});

Now if the currentUser is null or undefined, we should redirect users to the signin path. But how do we get currentUser? We can’t use firebase.auth().currentUser because on page refresh that property has not been set yet before the guard is triggered. We will have to use the onAuthStateChanged callback somehow. Let’s add a method to the firebase object after we initialize the firebase app.

firebase.initializeApp(firebaseConfig);

firebase.getCurrentUser = () => {
    return new Promise((resolve, reject) => {
        const unsubscribe = firebase.auth().onAuthStateChanged(user => {
            unsubscribe();
            resolve(user);
        }, reject);
    })
};

This method will return a Promise which resolves currentUser as soon as it is set. onAuthStateChangedwill trigger the callback immediately with either null or the user object if signed in. Then we unsubscribe to not listen for further changes.

Now we will update our beforeEach guard so that only paths that require authentication await this method.

router.beforeEach(async (to, from, next) => {
  const requiresAuth = to.matched.some(record => record.meta.requiresAuth);
  if (requiresAuth && !await firebase.getCurrentUser()){
    next('signin');
  }else{
    next();
  }
});

That’s all. This also simplifies getting the currentUser for components under the guarded routes, because we know firebase.auth().currentUser is set.

For full example check out this GitHub repository and demo at vue-routes-authentication.web.app