Actions

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Actions are the equivalent of methods in components. They can be defined with the actions property in defineStore() and they are perfect to define business logic:

export const useCounterStore = defineStore('counter', {
  state: () => ({
    count: 0,
  }),
  actions: {
    // since we rely on `this`, we cannot use an arrow function
    increment() {
      this.count++
    },
    randomizeCounter() {
      this.count = Math.round(100 * Math.random())
    },
  },
})

Like getters, actions get access to the whole store instance through this with full typing (and autocompletion ✨) support. Unlike getters, actions can be asynchronous, you can await inside of actions any API call or even other actions! Here is an example using Mande. Note the library you use doesn't matter as long as you get a Promise. You could even use the native fetch function (browser only):

import { mande } from 'mande'

const api = mande('/api/users')

export const useUsers = defineStore('users', {
  state: () => ({
    userData: null,
    // ...
  }),

  actions: {
    async registerUser(login, password) {
      try {
        this.userData = await api.post({ login, password })
        showTooltip(`Welcome back ${this.userData.name}!`)
      } catch (error) {
        showTooltip(error)
        // let the form component display the error
        return error
      }
    },
  },
})

You are also completely free to set whatever arguments you want and return anything. When calling actions, everything will be automatically inferred!

Actions are invoked like regular functions and methods:

<script setup>
const store = useCounterStore()
// call the action as a method of the store
store.randomizeCounter()
</script>

<template>
  <!-- Even on the template -->
  <button @click="store.randomizeCounter()">Randomize</button>
</template>

Accessing other stores actions

To consume another store, you can directly use it inside of the action:

import { useAuthStore } from './auth-store'

export const useSettingsStore = defineStore('settings', {
  state: () => ({
    preferences: null,
    // ...
  }),
  actions: {
    async fetchUserPreferences() {
      const auth = useAuthStore()
      if (auth.isAuthenticated) {
        this.preferences = await fetchPreferences()
      } else {
        throw new Error('User must be authenticated')
      }
    },
  },
})

Usage with the Options API

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For the following examples, you can assume the following store was created:

// Example File Path:
// ./src/stores/counter.js

import { defineStore } from 'pinia'

export const useCounterStore = defineStore('counter', {
  state: () => ({
    count: 0
  }),
  actions: {
    increment() {
      this.count++
    }
  }
})

With setup()

While Composition API is not for everyone, the setup() hook can make Pinia easier to work with while using the Options API. No extra map helper functions needed!

<script>
import { useCounterStore } from '../stores/counter'

export default defineComponent({
  setup() {
    const counterStore = useCounterStore()

    return { counterStore }
  },
  methods: {
    incrementAndPrint() {
      this.counterStore.increment()
      console.log('New Count:', this.counterStore.count)
    },
  },
})
</script>

Without setup()

If you would prefer not to use Composition API at all, you can use the mapActions() helper to map actions properties as methods in your component:

import { mapActions } from 'pinia'
import { useCounterStore } from '../stores/counter'

export default {
  methods: {
    // gives access to this.increment() inside the component
    // same as calling from store.increment()
    ...mapActions(useCounterStore, ['increment']),
    // same as above but registers it as this.myOwnName()
    ...mapActions(useCounterStore, { myOwnName: 'increment' }),
  },
}

Subscribing to actions

It is possible to observe actions and their outcome with store.$onAction(). The callback passed to it is executed before the action itself. after handles promises and allows you to execute a function after the action resolves. In a similar way, onError allows you to execute a function if the action throws or rejects. These are useful for tracking errors at runtime, similar to this tip in the Vue docs.

Here is an example that logs before running actions and after they resolve/reject.

const unsubscribe = someStore.$onAction(
  ({
    name, // name of the action
    store, // store instance, same as `someStore`
    args, // array of parameters passed to the action
    after, // hook after the action returns or resolves
    onError, // hook if the action throws or rejects
  }) => {
    // a shared variable for this specific action call
    const startTime = Date.now()
    // this will trigger before an action on `store` is executed
    console.log(`Start "${name}" with params [${args.join(', ')}].`)

    // this will trigger if the action succeeds and after it has fully run.
    // it waits for any returned promised
    after((result) => {
      console.log(
        `Finished "${name}" after ${
          Date.now() - startTime
        }ms.\nResult: ${result}.`
      )
    })

    // this will trigger if the action throws or returns a promise that rejects
    onError((error) => {
      console.warn(
        `Failed "${name}" after ${Date.now() - startTime}ms.\nError: ${error}.`
      )
    })
  }
)

// manually remove the listener
unsubscribe()

By default, action subscriptions are bound to the component where they are added (if the store is inside a component's setup()). Meaning, they will be automatically removed when the component is unmounted. If you also want to keep them after the component is unmounted, pass true as the second argument to detach the action subscription from the current component:

<script setup>
const someStore = useSomeStore()

// this subscription will be kept even after the component is unmounted
someStore.$onAction(callback, true)
</script>