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What are the differences between the Composition API used in Vue 3.0 and the Options API used in Vue 2.x?

The differences between Vue 3.0's Composition API and Vue 2.x's Options API are as follows:

Code Organization:

Composition API: Uses the setup function to centralize the management of a component's state and logic, making the code easier to read and maintain.
Options API: Distributes component state and logic across different options such as data, methods, computed, and watch.
Logic Reuse and Composition:

Composition API: Facilitates easier extraction and reuse of component logic without needing mixins or other abstraction mechanisms.
Options API: Typically requires the use of mixins or higher-order components to reuse logic, which can lead to naming conflicts and tight coupling between components.
Type Support:

Composition API: Being function-based, it integrates more easily with TypeScript (functional programming).
Options API: May require additional type declarations and decorators.
Reactivity Declaration:

Composition API: Explicitly creates reactive state using ref and reactive.
Options API: Reactive state is typically created implicitly within the data option.
Lifecycle Hooks:

Composition API: Lifecycle hooks like onMounted and onUpdated exist as functions within the setup function.
Options API: Lifecycle hooks are defined as component options, such as mounted and updated.
Template Usage:

Composition API: All variables and methods returned by the setup function can be directly used in the template.
Options API: Data and methods in the template need to be defined separately in data, computed, methods, etc.
Dependency Tracking:

Composition API: Provides more granular dependency tracking, where only the actual state in use triggers component updates.
Options API: May cause unnecessary component re-renders in certain scenarios.
Code Splitting and On-Demand Import:

Composition API: Facilitates easier code splitting and on-demand imports since related logic can be more easily organized together.
Options API: Code splitting and on-demand imports are usually more complex and redundant.
Readability and Maintainability:

Composition API: For complex components, it is usually easier to understand and maintain due to the centralized logic.
Options API: For simple components, it may be more intuitive as the API is dispersed.
Community and Ecosystem:

Composition API: As a new feature in Vue 3, it may take time to build an ecosystem around it.
Options API: Already has a mature community and abundant resources.
Both have their advantages and disadvantages, and Vue 3 also supports mixing the two, allowing developers to choose the API that best suits their specific needs.

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