Which VueJS lifecycle hook must Asynchronous HTTP requests be called in?

Question

I'd like to know how before I render a page, I want to send an async GET request to my server to retrieve data and populate the properties in data. I heard the best way to do this is to call the function that sends this request in one of the three lifecycle hooks Vue js offers that operate before the DOM is rendered. The three are beforeCreate(), created(), beforeMount(). Which one must this request be called in ideally? And why?

Answer 1

TL;DR in the general (and safe) case, use created().

Vue's initialization code is executed synchronously.

Technically, any ASYNChronous code you run in beforeCreate(), created(), beforeMount() will only respond after all of those hooks finish. See demo:

new Vue({    el: '#app',    beforeCreate() {      setTimeout(() => { console.log('fastest asynchronous code ever') }, 0);      console.log('beforeCreate hook done');    },    created() {      console.log('created hook done');    },    beforeMount() {      console.log('beforeMount hook done');    },    mounted() {      console.log('mounted hook done');    }  })

<script src="https://unpkg.com/vue/dist/vue.min.js"></script>  <div id="app">    Check the console.  </div>

In other words, if you make an Ajax call in beforeCreate(), no matter how fast the API responds, the response will only be processed way later, way after the created() has been executed.

What should guide your decision, then?

• Need just to trigger a call as soon as possible?
  • Use beforeCreate()
  • Why?
    • It runs sooner than any of those hooks, but...
• Need to read from or modify data right away?
  • Use created()
  • Why?
    • State is only initialized between beforeCreate() and created(), so if you assign some data before created(), it would be lost.
• Need anything that is generated after created()?
  • Use beforeMount()
  • Why?
    • I don't know anything that isn't available at created() and is available at beforeMount() other than the compiled this.$options.render render function (see source as well), so this case must really be a rare situation.

Answer 2

The vue-router docs have some advice for patterns to use when retrieving data from a server that is required for component render (see bottom for link).

To determine where to perform the GET request, they first ask if you want to navigate to the route before async GET request is initiated or after

If you want to fetch the data then navigate to the route (before navigation) then the docs suggest performing the async request in the beforeRouteEnter() guard on the incoming component making sure to call next() in beforeRouteEnter() once the async data request has been fulfilled. If you choose this pattern you will want to display some sort of loading indicator as the navigation to the route/rendering of the component will not occur until the data has been fetched.

If you want to navigate to the route then initiate the request (after navigation) then the docs suggest performing the request in the created() hook and using v-if to conditionally show either that the component is loading, an error has occurred, or the view once the data has arrived.

Highly recommend checking out the docs, they have code examples and its well written. https://router.vuejs.org/guide/advanced/data-fetching.html#fetching-before-navigation