scrollFetchSetupComponent.vue

// ...
<script>
import {
    value,
    watch,
    computed,
    onMounted,
    onUnmounted
} from 'vue-function-api'
import { fetchUserPosts } from '@/api'

export default {
  setup(props) {
    const pageOffset = value(0)
    const isLoading = value(false)
    const posts = value([])
    const count = computed(() => posts.value.length)
    const update = () => {
      pageOffset.value = window.pageYOffset
    }
    
    onMounted(() => window.addEventListener('scroll', update))
    onUnmounted(() => window.removeEventListener('scroll', update))
    
    watch(
      () => props.id,
      async id => {
        isLoading.value = true
        posts.value = await fetchUserPosts(id)
        isLoading.value = false
      }
    )
    
    return {
      isLoading,
      pageOffset,
      posts,
      count
    }
  }
}
</script>
// ...