TypeError：this.db.list（...）。subscribe不是一个函数

Question

I develop an Ionic 3.9 chat with Firebase and I have the following error:

TypeError: this.db.list(...).subscribe is not a function

Here is my code:

import { Component } from '@angular/core';
import { IonicPage, NavController, NavParams } from 'ionic-angular';
import { AngularFireDatabase } from 'angularfire2/database';

@IonicPage()
@Component({
    selector: 'page-consersation',
    templateUrl: 'conversation.html',
})
export class ConversationPage {
    username: string = '';
    message: string = '';
    _chatSubscription;
    s;
    messages;

    constructor(public db: AngularFireDatabase,
        public navCtrl: NavController, public navParams: NavParams) {
          this.username = this.navParams.get('username');
          this._chatSubscription = this.db.list('/conversation').subscribe( data => {
            this.messages = data;
          });
        }

    sendMessage() {
        this.db.list<any>('/conversation').push({
            username: 'romain',
            message: this.message
        }).then( () => {
            // message is sent
        });
        this.message = '';
    }
}

Can you help me please?

Answer 1

In this.db.list('/conversation').subscribe( you are missing something between the .list(...) and the .subscribe(...

What you're missing is either .valueChanges() or .snapshotChanges() ... You can read about the differences at the AngularFire2 documentation here .

I typically use .valueChanges() most often, so for a quick example with .valueChanges() your code would be:

this._chatSubscription = this.db.list('/conversation').valueChanges().subscribe( data => {
    this.messages = data;
);

EDIT - corrected code below. Not supposed to set a variable equal to the whole .subscribe ... Define your pointer/listener, and then subscribe to it separately.

this._chatSubscription = this.db.list('/conversation').valueChanges()
this._chatSubscription.subscribe( data => {
    this.messages = data;
);

2nd EDIT - after new error message that OP posted as answer. That new error looks like it's due to version conflicts - check out this question with multiple possible solutions .

Answer 2

When you're getting the following error polyfills.js:3 Uncaught TypeError: Object(...) is not a function... , try the following code below:

this._chatSubscription = this.db.object('/conversation').valueChanges().subscribe(data => {
  this.messages = data;
});