vue3-composition

Vue 3 Composition API

Baseline: Vue 3 Composition API with <script setup lang="ts">. Confirm the exact Vue version from the repository lockfile.

Non-negotiables

ALWAYS	NEVER
<script setup lang="ts"> for new components	Options API for new code
Composables named useXxx, return object	Return bare refs without naming
readonly() for state consumers must not mutate	Mutate props
Tailwind utilities for styling	Scoped CSS / inline styles (see tailwindcss4)

Decision tree

• Reusable stateful logic? → composable in composables/useXxx.ts
• Cross-tree dependency? → provide / inject with typed keys
• One-off UI state? → ref / reactive in the component
• Need Nuxt data fetching? → use nuxt4-frontend (useFetch / useAsyncData)

Core patterns

<script setup lang="ts">
interface Props {
  title: string
  count?: number
}
const props = withDefaults(defineProps<Props>(), { count: 0 })
const emit = defineEmits<{ save: [id: string] }>()

const open = ref(false)
</script>

<template>
  <section class="space-y-2">
    <h2 class="text-lg font-semibold">{{ props.title }}</h2>
    <button class="rounded-lg bg-slate-900 px-3 py-2 text-white" @click="open = !open">
      Toggle
    </button>
  </section>
</template>

// composables/useToggle.ts
export function useToggle(initial = false) {
  const on = ref(initial)
  function toggle() {
    on.value = !on.value
  }
  return { on: readonly(on), toggle }
}

Reactivity pitfalls

• Destructure props → lose reactivity unless toRefs / storeToRefs
• reactive + reassignment → prefer ref for reassignable state
• Async setup without await in Nuxt → prefer Nuxt async data APIs

Load next

When	Read
Nuxt-specific structure / data	nuxt4-frontend skill
Styling	tailwindcss4 skill

Pre-finish checklist

• script setup + TS
• No prop mutation
• Composables return named object
• No Options API in new files