Firebase和Vue Js生命周期挂钩

Question

I'm tring to load data from a particular user and push that data to specific input field. The path in Firebase is located at:

var query = db.ref('Clients/'+ clientName +'/form/');

I fecth data in the mounted() lifecycle hooks as follows:

mounted(){

// Grab current user logged in from Firebase
var user = firebaseApp.auth().currentUser;

if ( user ){
 // Grab displayName to use in path to retrieve that client's data
 var clientName = firebaseApp.auth().currentUser.displayName;

 // The path to that specific's client data
 var query = db.ref('Clients/'+ clientName+'/form/');

   query.once('value')
     .then((snapshot) => {

        // Get the client's location from Firebase and assign to  clientLocation data in the DOM
        this.clientLocation = snapshot.child('clientLocation').val();

     });
   }

}

When I make changes and SAVE MY CODE WITHOUT RELOADING the data gets pushed properly . However on reload I get the following error:

 Error in mounted hook: "TypeError: Cannot read property 'displayName' of null"

I played around with all the lifecyle hooks:

1. beforeCreate
2. created
3. beforeMount
4. mounted
5. beforeUpdate
6. updated
7. beforeDestroy
8. destroyed

But the data doesn't display. As it seems that the firebaseApp isn't "loaded" yet so I cannot fetch the "displayName" property value and thus cannot populate the path to the data.

How/when should I load this code that works but seems to run too early?

Answer 1

User information may need to be loaded/refreshed asynchronously. For this reason, always use an auth state listener to ensure your code runs when the user is available. Modified from the linked docs:

firebase.auth().onAuthStateChanged(function(user) {
  if (user) {
    // Grab displayName to use in path to retrieve that client's data
    var clientName = firebaseApp.auth().currentUser.displayName;

    // The path to that specific's client data
    var query = db.ref('Clients/'+ clientName+'/form/');

    var that = this;
    query.once('value').then((snapshot) => {
       // Get the client's location from Firebase and assign to  clientLocation data in the DOM
       that.clientLocation = snapshot.child('clientLocation').val();
    });
  }
});

You could put this in mounted() , but it should also work in any other lifecycle method.