---

name: vue-composition-api description: Master Vue Composition API - Composables, Reactivity Utilities, Script Setup, Provide/Inject sasmp_version: "1.3.0" bonded_agent: 02-vue-composition bond_type: PRIMARY_BOND version: "2.0.0" last_updated: "2025-01"

Vue Composition API Skill

Production-grade skill for mastering Vue's Composition API and building reusable, scalable logic.

Purpose

Single Responsibility: Teach composable design patterns, advanced reactivity utilities, and modern Vue 3 composition techniques.

Parameter Schema

interface CompositionAPIParams {
  topic: 'composables' | 'reactivity' | 'script-setup' | 'provide-inject' | 'all';
  level: 'beginner' | 'intermediate' | 'advanced';
  context?: {
    existing_knowledge?: string[];
    use_case?: string;
  };
}

Learning Modules

Module 1: Script Setup Basics

Prerequisites: vue-fundamentals
Duration: 1-2 hours
Outcome: Use <script setup> effectively

Topic	Concept	Exercise
Syntax	<script setup> shorthand	Convert Options API
defineProps	Type-safe props	Typed component
defineEmits	Type-safe events	Event handling
defineExpose	Public API	Component ref access

Module 2: Reactivity Deep Dive

Prerequisites: Module 1
Duration: 3-4 hours
Outcome: Master all reactivity utilities

Utility	When to Use	Exercise
ref()	Primitives	Counter state
reactive()	Objects	Form state
readonly()	Immutable exposure	Store state
toRef()	Single prop reference	Props handling
toRefs()	Destructure reactive	Store destructure
shallowRef()	Large objects	Performance opt
customRef()	Custom behavior	Debounced input

Module 3: Composables Architecture

Prerequisites: Modules 1-2
Duration: 4-5 hours
Outcome: Design production composables

Composable Anatomy:

// composables/useFeature.ts
export function useFeature(options?: Options) {
  // 1. State (refs)
  const state = ref(initialValue)

  // 2. Computed (derived)
  const derived = computed(() => transform(state.value))

  // 3. Methods (actions)
  function action() { /* ... */ }

  // 4. Lifecycle (setup/cleanup)
  onMounted(() => { /* setup */ })
  onUnmounted(() => { /* cleanup */ })

  // 5. Return (public API)
  return { state: readonly(state), derived, action }
}

Exercise	Composable	Features
Data Fetching	useFetch	loading, error, refetch
Local Storage	useStorage	sync, parse, stringify
Media Query	useMediaQuery	reactive breakpoints
Debounce	useDebounce	value, delay
Intersection	useIntersection	observer, cleanup

Module 4: Provide/Inject Patterns

Prerequisites: Module 3
Duration: 2 hours
Outcome: Share state across components

Pattern	Use Case	Example
Theme Provider	App-wide theming	Dark/light mode
Auth Context	User state	Auth provider
Config Injection	Feature flags	Runtime config
Form Context	Multi-step forms	Form validation

Module 5: Advanced Patterns

Prerequisites: Modules 1-4
Duration: 3-4 hours
Outcome: Expert-level composition

Pattern	Description	Exercise
Composable Composition	Composables using composables	useAuth + useFetch
State Machines	Finite state composables	useWizard
Plugin Pattern	Extend with plugins	useLogger plugin
Async Composables	Handle async setup	useAsyncData

Validation Checkpoints

Beginner Checkpoint

• Convert Options API to Composition
• Use ref and computed
• Write basic composable
• Use defineProps/Emits

Intermediate Checkpoint

• Build reusable composable
• Implement cleanup in composable
• Use provide/inject correctly
• Handle async in composables

Advanced Checkpoint

• Design composable library
• Compose multiple composables
• Implement SSR-safe composables
• Test composables in isolation

Retry Logic

const skillConfig = {
  maxAttempts: 3,
  backoffMs: [1000, 2000, 4000],
  onFailure: 'provide_simpler_example'
}

Observability

tracking:
  - event: composable_created
    data: [name, complexity_score]
  - event: pattern_learned
    data: [pattern_name, exercises_completed]
  - event: skill_mastery
    data: [modules_completed, project_quality]

Troubleshooting

Common Issues

Issue	Cause	Solution
Lost reactivity	Destructured reactive	Use toRefs()
inject undefined	Missing provider	Check tree hierarchy
Memory leak	No cleanup	Add onUnmounted cleanup
Type errors	Wrong generics	Specify type params

Debug Steps

1. Verify composable returns refs (not raw values)
2. Check provide/inject key matches
3. Confirm lifecycle hooks are in setup
4. Use Vue Devtools to inspect state

Unit Test Template

import { describe, it, expect } from 'vitest'
import { useCounter } from './useCounter'

describe('useCounter', () => {
  it('initializes with default value', () => {
    const { count } = useCounter()
    expect(count.value).toBe(0)
  })

  it('increments correctly', () => {
    const { count, increment } = useCounter()
    increment()
    expect(count.value).toBe(1)
  })

  it('resets to initial value', () => {
    const { count, increment, reset } = useCounter(5)
    increment()
    increment()
    reset()
    expect(count.value).toBe(5)
  })
})

Usage

Skill("vue-composition-api")

Related Skills

• vue-fundamentals - Prerequisite
• vue-pinia - State management
• vue-typescript - Type-safe composables

Resources

• Composition API Guide
• VueUse - Collection of composables
• Vue Patterns