mounted method is fired before data loaded - VueJS

Question

I'm using Vue Resource to retrieve an images collection from a REST API. The request is sent in the created hook of my Vue component.

The problem is, I'm trying to access the retrieved data in the mounted hook, but the data isn't loaded.

I get this error in the console:

[Vue warn]: Error in mounted hook: "TypeError: Cannot read property 'forEach' of undefined"

Here is my component:

<script>
export default {
  data() {
    return { imgs : '' };
  },
  created() {
    // the full url is declare in my main.js
    this.imgs = this.$resource('acf/v3/pages/4');

    this.imgs.query().then((response) => {
      console.log('success', response);
      this.imgs = response.data.acf.gallery;
    }, (response) => {
      console.log('erreur', response);
    });
  },
  mounted() {
    // get the ref="image" in my dom template
    let imgs = this.$refs.image;

    imgs.forEach((img) => {
      // I do some stuff with imgs
    });
  }
}
</script>

If I wrap a setTimeout around the content of mounted, everything works fine.

So, I don't understand how I can wait for my data to load before the mounted hook is executed. Isn't this the role of the Vue lifecycle hooks?

Answer 1

As shown in the Lifecycle Diagram of Vue instance. After Mounted Hook (which means we can access DOM), there is also beforeUpdate and updated hooks. These hooks can be used when data is changed. I think beforeUpdate or update hook can be used after getting data in created hook.

<script>
   export default {
      data() {
         return { imgs : '' };
       },
   created() {
    // the full url is declare in my main.js
    this.imgs = this.$resource('acf/v3/pages/4');

    this.imgs.query().then((response) => {
        console.log('success', response);
        this.imgs = response.data.acf.gallery;
       }, (response) => {
         console.log('erreur', response);
     });
   },
  // here we can use beforeUpdate or updated hook instead of mounted
  beforeUpdate() {
    // get the ref="image" in my dom template
    let imgs = this.$refs.image;

    imgs.forEach((img) => {
    // I do some stuff with imgs
   });
 }
}

I hope this helps.