• Understanding the Composition API
  • Why Use the Composition API?
• Getting Started
  • Basic Setup
  • Reactive State Management
• Creating Composables
  • Using Composables
• Advanced Patterns
  • Computed Properties
  • Watchers
• Best Practices
  • 1. Keep Composables Focused
  • 2. Consistent Naming Conventions
  • 3. Type Safety
• Common Pitfalls to Avoid
• Performance Optimization
  • 1. Lazy Loading Components
  • 2. Memo-ization
• Testing Composition API Code
• Migration Strategies
• Conclusion

[TOC]

Vue.js 3 Composition API: A Complete Guide for 2024

The Vue.js 3 Composition API represents a paradigm shift in how we write Vue applications. This comprehensive guide will help you master this powerful feature and understand when and how to use it effectively.

#Understanding the Composition API

The Composition API provides a new way to organize component logic in Vue.js applications. Instead of spreading related code across different options, you can group it together based on functionality.

#Why Use the Composition API?

1. Better TypeScript Support
2. More Flexible Code Organization
3. Better Code Reuse
4. Improved Runtime Performance

#Getting Started

#Basic Setup

import { ref, onMounted } from 'vue'

export default {
  setup() {
    // Reactive state
    const count = ref(0)

    // Methods
    const increment = () => {
      count.value++
    }

    // Lifecycle hooks
    onMounted(() => {
      console.log('Component mounted')
    })

    // Expose to template
    return {
      count,
      increment
    }
  }
}

#Reactive State Management

import { ref, reactive } from 'vue'

export default {
  setup() {
    // Using ref for primitive values
    const name = ref('John')

    // Using reactive for objects
    const user = reactive({
      firstName: 'John',
      lastName: 'Doe',
      age: 30
    })

    return {
      name,
      user
    }
  }
}

#Creating Composables

Composables are the Composition API's way of reusing stateful logic:

// useCounter.js
import { ref } from 'vue'

export function useCounter(initialValue = 0) {
  const count = ref(initialValue)

  const increment = () => {
    count.value++
  }

  const decrement = () => {
    count.value--
  }

  return {
    count,
    increment,
    decrement
  }
}

#Using Composables

import { useCounter } from './composables/useCounter'

export default {
  setup() {
    const { count, increment, decrement } = useCounter(10)

    return {
      count,
      increment,
      decrement
    }
  }
}

#Advanced Patterns

#Computed Properties

import { ref, computed } from 'vue'

export default {
  setup() {
    const firstName = ref('John')
    const lastName = ref('Doe')

    const fullName = computed(() => {
      return `${firstName.value} ${lastName.value}`
    })

    return {
      firstName,
      lastName,
      fullName
    }
  }
}

#Watchers

import { ref, watch } from 'vue'

export default {
  setup() {
    const searchQuery = ref('')

    watch(searchQuery, async (newValue, oldValue) => {
      if (newValue.length >= 3) {
        await performSearch(newValue)
      }
    })

    return {
      searchQuery
    }
  }
}

#Best Practices

#1. Keep Composables Focused

Create small, focused composables that handle one specific concern:

// Good
function useUserAuthentication() { ... }
function useNotifications() { ... }

// Avoid
function useUserAuthenticationAndNotifications() { ... }

#2. Consistent Naming Conventions

• Prefix composables with 'use'
• Use clear, descriptive names
• Keep naming consistent across your application

#3. Type Safety

interface User {
  id: number
  name: string
  email: string
}

function useUser() {
  const user = ref<User | null>(null)

  const fetchUser = async (id: number): Promise<void> => {
    user.value = await api.getUser(id)
  }

  return {
    user,
    fetchUser
  }
}

#Common Pitfalls to Avoid

1. Forgetting .value with refs
2. Destructuring reactive objects
3. Not properly typing composables
4. Overusing global state
5. Creating too large composables

#Performance Optimization

#1. Lazy Loading Components

const MyLargeComponent = defineAsyncComponent(() =>
  import('./components/MyLargeComponent.vue')
)

#2. Memo-ization

import { computed } from 'vue'

const memoizedValue = computed(() => {
  return expensiveOperation(dependencyValue.value)
})

#Testing Composition API Code

import { mount } from '@vue/test-utils'
import { useCounter } from './useCounter'

test('useCounter', () => {
  const wrapper = mount({
    template: '<div>{{ count }}</div>',
    setup() {
      return {
        ...useCounter()
      }
    }
  })

  expect(wrapper.text()).toBe('0')
})

#Migration Strategies

When moving from Options API to Composition API:

1. Start with new features
2. Gradually refactor existing components
3. Create composables for shared logic
4. Update tests as you go
5. Document patterns and decisions

#Conclusion

The Vue.js 3 Composition API offers a more flexible and powerful way to organize component logic. By following these patterns and best practices, you can create more maintainable and scalable Vue applications.

Key takeaways:

• Use composables for code reuse
• Maintain type safety
• Follow consistent patterns
• Test thoroughly
• Optimize performance
• Document your code

Happy coding! 🚀