Handle your promises with style ๐
Help me keep working on Open Source in a sustainable way ๐. Help me with as little as $1 a month, sponsor me on Github.
npm install vue-promised
# or
yarn add vue-promised
When dealing with asynchronous requests like fetching content through API calls, you may want to display the loading state with a spinner, handle the error and even hide everything until at least 200ms have been elapsed so the user doesn't see a loading spinner flashing when the request takes very little time. This is quite some boilerplate, and you need to repeat this for every request you want:
<template>
<div>
<p v-if="error">Error: {{ error.message }}</p>
<p v-else-if="isLoading && isDelayElapsed">Loading...</p>
<ul v-else-if="!isLoading">
<li v-for="user in data">{{ user.name }}</li>
</ul>
</div>
</template>
<script>
export default {
data: () => ({
isLoading: false,
error: null,
data: null,
isDelayElapsed: false,
}),
methods: {
fetchUsers() {
this.error = null
this.isLoading = true
this.isDelayElapsed = false
getUsers()
.then((users) => {
this.data = users
})
.catch((error) => {
this.error = error
})
.finally(() => {
this.isLoading = false
})
setTimeout(() => {
this.isDelayElapsed = true
}, 200)
},
},
created() {
this.fetchUsers()
},
}
</script>
๐ Compare this to the version using Vue Promised that handles new promises.
That is quite a lot of boilerplate and it's not handling cancelling on going requests when fetchUsers
is called again. Vue Promised encapsulates all of that to reduce the boilerplate.
Check the Changelog for breaking changes. v2 exposes the same Promised
and a new usePromise
function on top of that.
import { Promised, usePromise } from 'vue-promised'
Vue.component('Promised', Promised)
export default {
setup() {
const usersPromise = ref(fetchUsers())
const promised = usePromise(usersPromise)
return {
...promised,
// spreads the following properties:
// data, isPending, isDelayElapsed, error
}
},
}
Vue Promised also exposes the same API via a component named Promised
.
In the following examples, promise
is a Promise but can initially be null
. data
contains the result of the promise. You can of course name it the way you want:
<template>
<Promised :promise="usersPromise">
<!-- Use the "pending" slot to display a loading message -->
<template v-slot:pending>
<p>Loading...</p>
</template>
<!-- The default scoped slot will be used as the result -->
<template v-slot="data">
<ul>
<li v-for="user in data">{{ user.name }}</li>
</ul>
</template>
<!-- The "rejected" scoped slot will be used if there is an error -->
<template v-slot:rejected="error">
<p>Error: {{ error.message }}</p>
</template>
</Promised>
</template>
<script>
export default {
data: () => ({ usersPromise: null }),
created() {
this.usersPromise = this.getUsers()
},
}
</script>
The pending
slot can also receive the data that was previously available:
<Promised :promise="usersPromise">
<template v-slot:pending="previousData">
<p>Refreshing</p>
<ul>
<li v-for="user in previousData">{{ user.name }}</li>
</ul>
</template>
<template v-slot="data">
<ul>
<li v-for="user in data">{{ user.name }}</li>
</ul>
</template>
</Promised>
Although, depending on the use case, this could create duplication and using a combined
slot would be a better approach.
You can also provide a single combined
slot that will receive a context with all relevant information. That way you can customize the props of a component, toggle content with your own v-if
but still benefit from a declarative approach:
<Promised :promise="promise">
<template v-slot:combined="{ isPending, isDelayElapsed, data, error }">
<pre>
pending: {{ isPending }}
is delay over: {{ isDelayElapsed }}
data: {{ data }}
error: {{ error && error.message }}
</pre>
</template>
</Promised>
This allows to create more advanced async templates like this one featuring a Search component that must be displayed while the searchResults
are being fetched:
<Promised :promise="searchResults" :pending-delay="200">
<template v-slot:combined="{ isPending, isDelayElapsed, data, error }">
<div>
<!-- data contains previous data or null when starting -->
<Search :disabled-pagination="isPending || error" :items="data || []">
<!-- The Search handles filtering logic with pagination -->
<template v-slot="{ results, query }">
<ProfileCard v-for="user in results" :user="user" />
</template>
<!--
Display a loading spinner only if an initial delay of 200ms is elapsed
-->
<template v-slot:loading>
<MySpinner v-if="isPending && isDelayElapsed" />
</template>
<!-- `query` is the same as in the default slot -->
<template v-slot:noResults="{ query }">
<p v-if="error" class="error">Error: {{ error.message }}</p>
<p v-else class="info">No results for "{{ query }}"</p>
</template>
</Search>
</div>
</template>
</Promised>
isPending
: istrue
while the promise is in a pending status. Becomesfalse
once the promise is resolved or rejected. It is reset totrue
when thepromise
prop changes.isDelayElapsed
: istrue
once thependingDelay
is over or ifpendingDelay
is 0. Becomesfalse
after the specified delay (200 by default). It is reset when thepromise
prop changes.data
: contains the last resolved value frompromise
. This means it will contain the previous succesfully (non cancelled) result.error
: contains last rejection ornull
if the promise was fullfiled.
There are different ways to provide a promise to Promised
. The first one, is setting it in the created hook:
export default {
data: () => ({ promise: null }),
created() {
this.promise = fetchData()
},
}
But most of the time, you can use a computed property. This makes even more sense if you are passing a prop or a data property to the function returning a promise (fetchData
in the example):
export default {
props: ['id'],
computed: {
promise() {
return fetchData(this.id)
},
},
}
You can also set the promise
prop to null
to reset the Promised component to the initial state: no error, no data, and pending:
export default {
data: () => ({ promise: null }),
methods: {
resetPromise() {
this.promise = null
},
},
}
usePromise
returns an object of Ref
representing the state of the promise.
const { data, error, isPending, isDelayElapsed } = usePromise(fetchUsers())
Signature:
function usePromise<T = unknown>(
promise: Ref<Promise<T> | null | undefined> | Promise<T> | null | undefined,
pendingDelay?: Ref<number | string> | number | string
): {
isPending: Ref<boolean>
isDelayElapsed: Ref<boolean>
error: Ref<Error | null | undefined>
data: Ref<T | null | undefined>
}
Promised
will watch its prop promise
and change its state accordingly.
Name | Description | Type |
---|---|---|
promise |
Promise to be resolved | Promise |
pendingDelay |
Delay in ms to wait before displaying the pending slot. Defaults to 200 |
`Number |
All slots but combined
can be used as scoped or regular slots.
Name | Description | Scope |
---|---|---|
pending |
Content to display while the promise is pending and before pendingDelay is over | previousData : previously resolved value |
default | Content to display once the promise has been successfully resolved | data : resolved value |
rejected |
Content to display if the promise is rejected | error : rejection reason |
combined |
Combines all slots to provide a granular control over what should be displayed | context See details |