javascript - Calling 'this' inside of firebase once function - Stack Overflow

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So I am creating a Vuejs application and I am trying to fetch firebase data on ponent mount. That is working, but I try to write the value into a vuejs data property. For this I would only call this.property = snapshot.val(); inside the firebase function (see code below) but that is not working: this is undefined

So my code just is:

export default {
  data() {
    return {
      imageList: "No images!"
    }
  },
  mounted() {
    if (!firebase.apps.length) {
      // Initialize Firebase
      var config = {
        ...
      };

      firebase.initializeApp(config);

      var database = firebase.database();
      var ref = database.ref("images").orderByChild("date");


    firebase.database().ref("images/").once('value').then(function(snapshot) {
        this.imageList= snapshot.val();
      });
    }
  }
}

I tried calling this.imageList= snapshot.val(); outside of the function with a variable to store the value, and 'this' wasn't undefined anymore, but the data wasn't there because the request hasn't finished yet.

So basically I want to get the snapshot.val(); into this.imageList!

Thanks in advance.

So I am creating a Vuejs application and I am trying to fetch firebase data on ponent mount. That is working, but I try to write the value into a vuejs data property. For this I would only call this.property = snapshot.val(); inside the firebase function (see code below) but that is not working: this is undefined

So my code just is:

export default {
  data() {
    return {
      imageList: "No images!"
    }
  },
  mounted() {
    if (!firebase.apps.length) {
      // Initialize Firebase
      var config = {
        ...
      };

      firebase.initializeApp(config);

      var database = firebase.database();
      var ref = database.ref("images").orderByChild("date");


    firebase.database().ref("images/").once('value').then(function(snapshot) {
        this.imageList= snapshot.val();
      });
    }
  }
}

I tried calling this.imageList= snapshot.val(); outside of the function with a variable to store the value, and 'this' wasn't undefined anymore, but the data wasn't there because the request hasn't finished yet.

So basically I want to get the snapshot.val(); into this.imageList!

Thanks in advance.

• javascript
• firebase
• firebase-realtime-database
• vue.js
• vue-ponent

Share Improve this question Follow asked Jul 20, 2017 at 20:00 Janis JansenJanis Jansen 1,03511 gold badge1818 silver badges4040 bronze badges

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3 Answers 3

Sorted by: Reset to default 10

You can use es6 arrow function syntax to solve the issue.

firebase.database().ref("images/").once('value').then((snapshot) => {
    this.imageList= snapshot.val();
});

or bind this to the context of the function.

var that = this;

Use an arrow function, a closure, or bind.

firebase.database().ref("images/").once('value').then(snapshot => {
  this.imageList= snapshot.val();
});

See How to access the correct this inside a callback.

You can use bind as well.

firebase.database().ref('images/').once('value').then(function(snapshot) {
  this.imageList = snapshot.val()
}.bind(this))

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