14

I'm trying to understand the purpose of composables. I have a simple composable like this and was trying to watch state from a Pinia store where the watch does not trigger:

import { ref, watch, computed } from "vue";
import { storeToRefs } from "pinia";
import useFlightsStore from "src/pinia/flights.js";
import usePassengersStore from "src/pinia/passengers.js";

export function useFlight() {
    const route = useRoute();

    const modalStore = useModalStore();
    const flightsStore = useFlightsStore();
    const { selection } = storeToRefs(flightsStore);

    const passengersStore = usePassengersStore();
    const { passengers, adults, children, infants } =
        storeToRefs(passengersStore);

    watch([adults, children, infants], (val) => console.log('value changes', val))

Where as the same thing in a Vue component works as expected.

So we cannot watch values inside composables?

Dom
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Riza Khan
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4 Answers4

23

I think you can watch values inside composables.

But, to watch a pinia state it has to be inside an arrow function:

watch(() => somePiniaState, (n) => console.log(n, " value changed"));

It's like watching a reactive object.

I believe this should be documented better. In Pinia documentation we can read how to watch the whole store or how to subscribe to a store but not how to watch a single state property inside a component or composable.

Also, the docs are somewhat shy in explaining that you can watch a property inside a store using setup() way of describing a store.

More on this here: https://github.com/vuejs/pinia/discussions/794#discussioncomment-1643242

This error also silently fails (or does not execute), which is not helpful...

Dom
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    Tried this and still no results – Riza Khan Apr 22 '22 at 15:22
  • Can confirm, so far state variables don't have any reactivity outside the store for me, but getters do though. – StrikeAgainst Apr 29 '22 at 22:04
  • Is it using the option api? I changed my code to use the script setup and the reactivity works out of the box. It's really easy to access states as well. It simplified my code a lot, even though I love the option api. – Alqua Nov 16 '22 at 17:08
  • Where and how is the line with `watch(()=>somePiniaState...)` to be integrated in a component? A more detailed example would be nice... – Dirk Schumacher Apr 10 '23 at 18:38
13

I needed to watch a specific state attribute in one of my components but I didn't find my use case on the official documentation. I used a mix between a watch and storeToRefs to do it.

// Option API
<script>
import { usePlaylistsStore } from '@/stores/playlists'
import { storeToRefs } from 'pinia'
export default {
    name: 'PlaylistDetail',

    setup() {
        const playlistsStore = usePlaylistsStore()
        const { selectedGenres } = storeToRefs(playlistsStore)
        return { selectedGenres }
    },
    watch: {
        selectedGenres(newValue, oldValue) {
            // do something
        }
    }
}
</script>

// Composition API
<script setup>
import { usePlaylistsStore } from '@/stores/playlists'
import { storeToRefs } from 'pinia'
import { computed, watch } from 'vue'

const playlistsStore = usePlaylistsStore()
const { selectedGenres } = storeToRefs(playlistsStore)

watch(() => selectedGenres, (newValue, oldValue) {
    // do something
})
</script>
Samuel RIGAUD
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3

There are 3 options for you to be able to use the watch in this context:

Option 1: Return in setup

    setup() {
        const store = useStore()
        const { piniaVariable } = storeToRefs(store)
        return { piniaVariable }
    },
    watch: {
        piniaVariable (newValue, oldValue) {
            // do something
        }
    }

Option 2: Direct Access

watch: {
        'yourStore.piniaVariable' (newValue, oldValue) {
            // do something
        }
    }

Option 3: Computed Property

computed: {
    piniaVariable() {
        return useYourStore.piniaVariable
    }

    watch: {
        piniaVariable (newValue, oldValue) {
            // do something
        }
    }

}
Mithsew
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1

By default watches in Vue are shallow watches. In order to watch the nested property change you have to set deep option of the watch to true.

watch(state, (newState, oldState) => {
// do stuff
}, { deep: true})

more on this

Ratnadip Das
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