**How to Implement Component-Level State Sharing Using Composition API in Vue 3** **Answer:** In Vue 3, the Composition API enables state sharing between components by combining `provide/inject` mechanisms or creating reusable reactive state modules (often referred to as "composables"). The more common and recommended approach is to define an independent reactive object (e.g., using `reactive` or `ref`) and import it into multiple components to achieve state sharing. **Example:** 1. **Create a Shared State Module (store.js):** ```js import { reactive, readonly } from 'vue'; const state = reactive({ count: 0 }); const increment = () => { state.count++; }; export const useCounterStore = () => { return { state: readonly(state), increment }; }; ``` 2. **Use the Module in Any Component:** ```vue ``` **Parsing:** - Vue 3's Composition API allows encapsulating logic into functions (i.e., composable functions), which can be reused across multiple components. - By using `reactive` to create reactive state and `readonly` to prevent direct external modification, the state is only updated through defined methods (similar to Vuex's mutations). - This approach does not require introducing Vuex or Pinia (though Pinia is the official recommended state management library for larger applications). It is suitable for simple state sharing in smaller projects. - For more complex state management (e.g., time travel, plugin systems), Pinia is recommended. **Note:** This method leverages the singleton nature of JavaScript modules—i.e., importing the same module multiple times results in shared state.