mounted method is fired before data loaded - VueJS

Since the this.imgs.query() call is async, your mounted hook is being called before the then handler is setting this.imgs (which I'm assuming is being bound with v-for to an element in your template with an attribute ref="image"). So, even though the component has been mounted to the DOM, the $refs have not been set up yet.

I would make a method to "do some stuff with imgs" and then call that method in a $nextTick callback in the then handler of the async call. The callback passed to $nextTick will be "executed after the next DOM update cycle", meaning the $refs will be set up at that point.

<script>export default {  data() {    return { imgs: '' };  },  created() {    // the full url is declare in my main.js    this.imgs = this.$resource('acf/v3/pages/4');    this.imgs.query().then((response) => {      console.log('success', response);      this.imgs = response.data.acf.gallery;      this.$nextTick(() => this.doStuffWithImgs());    }, (response) => {      console.log('erreur', response);    });  },  methods: {    doStuffWithImgs() {      // get the ref="image" in my dom template      let imgs = this.$refs.image;      imgs.forEach((img) => {        // I do some stuff with imgs      });    }  }}</script>

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   }); }}