vue3 setup

Vue 3 introduces a new function called `setup` to replace the options-based API used in Vue 2. The `setup` function allows you to initialize component state, define computed properties, and set up component lifecycle hooks.

In Vue 3, the `setup` function is executed before the component is created, providing a more explicit and flexible way to define component logic. Here's an example of how to use the `setup` function:

<template>
  <div>
    <p>{{ message }}</p>
    <button @click="increment">Increment</button>
  </div>
</template>

<script>
import { ref } from 'vue';

export default {
  setup() {
    const message = ref('Hello Vue 3');
    
    function increment() {
      message.value += '!';
    }

    return {
      message,
      increment
    };
  }
};
</script>

In the example above, we import `ref` from the `vue` package, which allows us to create a reactive reference. Inside the `setup` function, we declare a `message` variable using `ref`, and a function called `increment` that appends an exclamation mark to the message. We then return these variables and functions as an object from the `setup` function.

By using the `setup` function, you can access reactive properties and functions directly in the template without the need for the `this` context. This makes the code more concise and easier to read.

I hope this helps! Let me know if you have any further questions.