store.ts

export const useMainStore = defineStore('main', () => {
  const count = ref(0)
  const arr = ref([1, 2, 3])

  // 基本和直接在setup中书写js一样
  const changeArr = (number: number) => {
    count.value += number
    arr.value.push(123)
  }

  return { count, arr, changeArr }
})

HelloWorld.vue

<template>
  <p>Count: {{ count }}</p>
</template>

<script setup lang="ts">
  import { useMainStore } from './store.ts'

  const mainStroe = useMainStore()
  const { count } = mainStroe

  function changeCount(number: number) {
    mainStroe.changeArr(number)
  }
</script>