How do I access Vue instance inside a js file in Vue3?

In Vue 3, accessing the Vue instance differs from Vue 2 primarily due to the introduction of the Composition API, which altered the organization of component code. In Vue 3, directly accessing the Vue instance via this is not typically used as in Vue 2, as the Composition API encourages organizing logic using the setup function and other Composition API functions.

Using the setup Function to Access the Vue Instance

In Vue 3 components, the setup function is a new option that executes before component creation, used for defining reactive state and functions. Within the setup function, direct access to the current component instance via this is not possible. However, Vue 3 provides a method to retrieve the current component instance within the setup function using the getCurrentInstance function.

Here is a simple example:

javascript
import { defineComponent, ref, getCurrentInstance } from 'vue';

export default defineComponent({
    setup() {
        const count = ref(0);
        const instance = getCurrentInstance();
        
        console.log(instance); // This outputs the current component instance information
        
        // Access component properties via the instance
        console.log(instance.props);
        console.log(instance.slots);
        
        const increment = () => {
            count.value++;
        };
        
        return {
            count,
            increment,
        };
    }
});

Important Notes

• The getCurrentInstance function is primarily used to access internal component instance properties such as props, slots, and emit. However, the official documentation advises against using it, as it exposes internal APIs that may change in future versions.
• In most cases, manage state through props, context, or Composition API functions like ref and reactive, rather than relying on the component instance.

Using the methods described, you can access and manipulate the component instance in Vue 3 components, but you should exercise caution and adhere to Vue 3 best practices.