As we saw in the The almighty components section, our component-based app will have a tree of components, and we need them to communicate with each other. For now, we will only focus on descending, parent-to-child communication. This is accomplished with "props".

Our top-bar component needs to know who the players are, which one is currently playing, and what the current turn number is. So, we will need three props--players, currentPlayerIndex, and turn.

To add props to a component definition, use the props option. For now, we will simply list the names of our props. However, you should know that there is a more detailed notation with an object instead, which we will cover in the next chapters.

1. Let's add the props to our component:

      Vue.component('top-bar', {
        // ...
        props: ['players', 'currentPlayerIndex', 'turn'],
      })

In the parent component, which is the root application, we can set the props value the exact same way we would for HTML attributes.

2. Go ahead and use the v-bind shorthand to wire the props value with the app data in the main template:

      <top-bar :turn="turn" :current-player-index="currentPlayerIndex"         
      :players="players" />

Now, we can use the props in our top-bar component just like data properties. For example, you could write something like this:

Vue.component('top-bar', {
  // ...
  created () {
    console.log(this.players)
  },
})

This would print the players array sent by the parent component (our app) in the browser console.