Converting Vue 2 Options API to Vue 3 Composition API involves restructuring the code from an object-based approach to a function-based approach. Here’s an example of how you can convert a simple Vue 2 Options API component to a Vue 3 Composition API component:

Vue 2 Options API Component:
<template>
<div>{{ message }}</div>
</template>

<script>
export default {
data() {
return {
message: “Hello World”,
};
},
};
</script>

Vue 3 Composition API Component:

<template>
<div>{{ message }}</div>
</template>

<script>
import { ref } from ‘vue’;

export default {
setup() {
const message = ref(“Hello World”);
return {
message,
};
},
};
</script>

Here are the steps involved in the conversion process:

1. Import the required functions from the Vue 3 Composition API library. In this example, we imported ref function.
2. Change the data() function to setup(). setup() function is a new function in Vue 3 Composition API that replaces the Options API lifecycle hooks.
3. Instead of returning an object with properties in setup(), define variables using the functions from the Composition API. In this example, we used the ref function to define a reactive variable message.
4. Return an object with variables defined in setup().

By using the Composition API, you can take advantage of the new features of Vue 3, such as reactive and computed properties, lifecycle hooks and custom hooks.