Basic reactive store with Vue 3: https://v3.vuejs.org/api/basic-reactivity.html

consumer.js

import store from './store.js'

console.log(store.state.hello) // '🌍'
store.greet('🌌')
console.log(store.state.hello) // '🌌'

console.log(store.state.cool) // Set('🍍')
store.addCool('🍌')
console.log(store.state.cool) // Set('🍍', '🍌')

store.js

import { reactive } from 'vue'

export default {
  state: reactive({
    hello: '🌍',
    cool: new Set('🍍')
  }),
  
  greet (name) {
    this.state.hello = name
  },
  
  addCool (stuff) {
    this.state.cool.add(stuff)
  }
}