Which VueJS lifecycle hook must Asynchronous HTTP requests be called in?
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:
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...
- Use
- Need to read from or modify
dataright away?- Use
created() - Why?
- Use
- Need anything that is generated after
created()?- Use
beforeMount() - Why?
- I don't know anything that isn't available at
created()and is available atbeforeMount()other than the compiledthis.$options.renderrender function (see source as well), so this case must really be a rare situation.
- I don't know anything that isn't available at
- Use
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
As mentioned above, the key issue that exists in both Vue and React is, if you make a network request and the data arrives before the component is created, there is no instance to set the data to.
beforeCreated is similar to React's componentWillMount. You generally wouldn't want to execute a network request here because you might get your data back before the component exists. It's like setting this.data = data but there is no component, so this doesn't exist yet.
A better place in React is componentDidMount, but we don't care about that. In Vue, a better place is created because the component has been created already, so this exists.
Here is an example:
<template> <div> <span v-if="error">{{ error }}</span><br> I like:<br> {{ data }} </div></template><script>export default { data() { return { data: '', error: undefined, } }, async created() { try { const response = await axios.get('/endpoint/stuff') this.data = response } catch (err) { this.error = err } },}</script>