Why should you not use async in the onCreated hook? Where is it more appropriate to make asynchronous requests?

In Vue.js (especially Vue 2), it is not recommended to make the created function asynchronous (async) because Vue does not wait for promises in lifecycle hooks, which can lead to unpredictable component behavior. Asynchronous code inside created will not be handled correctly, and the component's state may not be ready at render time.

It is better to perform asynchronous requests in the mounted hook, which is called after the component has been mounted to the DOM. This guarantees that all reactive properties and the template are already initialized, and you can safely update data after receiving a response.

Example:

export default {
  data() {
    return { items: [] };
  },
  mounted() {
    fetch('/api/items')
      .then(response => response.json())
      .then(data => {
        this.items = data;
      });
  }
}

If using Vue 3 with Composition API, asynchronous operations are usually performed inside onMounted or setup using async functions, but taking into account reactivity features.