What's the advantages of using this library ?

[asafyish]

Not trying to offend, trying to understand do we really need a state management library for Vue 3?
I mean, the example code in the first page:

import { createStore } from 'pinia'

export const useMainStore = createStore({
  // name of the store
  // it is used in devtools and allows restoring state
  id: 'main',
  // a function that returns a fresh state
  state: () => ({
    counter: 0,
    name: 'Eduardo',
  }),
  // optional getters
  getters: {
    doubleCount: (state, getters) => state.counter * 2,
    // use getters in other getters
    doubleCountPlusOne: (state, { doubleCount }) => doubleCount.value * 2,
  },
  // optional actions
  actions: {
    reset() {
      // `this` is the store instance
      this.state.counter = 0
    },
  },
})

Can be replaced with:

import { computed, reactive } from '@vue/composition-api';

const state = reactive({
    counter: 0,
    name: 'Eduardo',
});

// Getters / Computed
const doubleCount = computed(() => state.counter * 2);
const doubleCountPlusOne = computed(() => doubleCount * 2 + 1);

// Actions
const reset = () => state.counter = 0;

export { state, doubleCount, doubleCountPlusOne, reset };

and it will work mostly the same.
Are there any advantages for pinia over the example I attached ?

[posva]

It's fine. Most are highlighted in the Readme but not compared with a vanilla approach, so I understand why it may not be clear

• SSR support (your example doesn't work with concurrent requests)
• devtools support
• grouped information, structure, convention

Some things can still get even better