Vue 3 Functional Components

Vue 3 Functional Components are a type of component in Vue.js, a popular JavaScript framework for building user interfaces. These components are purely functional, meaning they don't have any internal state or lifecycle methods. Instead, they are simply functions that take in props and return a virtual DOM, which is a lightweight copy of the actual DOM. The main advantage of functional components is their simplicity and performance. Because they don't have any internal state or lifecycle methods, they are much simpler to understand and use. They are also faster to render, because Vue.js can skip the component initialization process and go straight to rendering the virtual DOM. In Vue 3, functional components are defined using the `functional` keyword in the component definition. Here's an example: 

export default {
  functional: true,
  props: ['message'],
  render(createElement, context) {
    return createElement('div', context.props.message);
  }
}

In this example, the component takes in a `message` prop and renders it inside a `div`. The `createElement` function is used to create the virtual DOM nodes.

One thing to note is that functional components in Vue 3 do not have access to the `this` keyword, because they are not instances of Vue. Instead, they receive a second argument in the render function, called `context`, which provides access to the props, slots, parent component, and other information.

Functional components are a powerful tool in Vue.js, especially for simple, stateless components. However, they are not suitable for every situation. If you need to manage state, use lifecycle methods, or access the `this` keyword, you should use a regular Vue component instead.