Defining a Store

Before diving into core concepts, we need to know that a store is defined using defineStore() and that it requires a unique name, passed as the first argument:

import { defineStore } from 'pinia'

// useStore could be anything like useUser, useCart
// the first argument is a unique id of the store across your application
export const useStore = defineStore('main', {
  // other options...
})

This name, also referred as id, is necessary and is used by Pinia to connect the store to the devtools. Naming the returned function use... is a convention across composables to make its usage idiomatic.

Using the store

We are defining a store because the store won't be created until useStore() is called inside of setup():

import { useStore } from '@/stores/counter'

export default {
  setup() {
    const store = useStore()

    return {
      // you can return the whole store instance to use it in the template
      store,
    }
  },
}

You can define as many stores as you want and you should define each store in a different file to get the most out of pinia (like automatically allow your bundle to code split and TypeScript inference).

If you are not using setup components yet, you can still use Pinia with map helpers.

Once the store is instantiated, you can access any property defined in state, getters, and actions directly on the store. We will see these in detail in the next pages but autocompletion will help you.

Note that store is an object wrapped with reactive, meaning there is no need to write .value after getters but, like props in setup, we cannot destructure it:

export default defineComponent({
  setup() {
    const store = useStore()
    // ❌ This won't work because it breaks reactivity
    // it's the same as destructuring from `props`
    const { name, doubleCount } = store

    name // "eduardo"
    doubleCount // 2

    return {
      // will always be "eduardo"
      name,
      // will always be 2
      doubleCount,
      // this one will be reactive
      doubleValue: computed(() => store.doubleCount),
      }
  },
})

In order to extract properties from the store while keeping its reactivity, you need to use storeToRefs(). It will create refs for any reactive property. This is useful when you are only using state from the store but not calling any action:

import { storeToRefs } from 'pinia'

export default defineComponent({
  setup() {
    const store = useStore()
    // `name` and `doubleCount` are reactive refs
    // This will also create refs for properties added by plugins
    // but skip any action or non reactive (non ref/reactive) property
    const { name, doubleCount } = storeToRefs(store)

    return {
      name,
      doubleCount
    }
  },
})