import Vue from 'vue'
import App from './app.vue'

new Vue({
    el: 'body',
    components: { App }
})

<template>
    <div class="message">{{ message }}</div>
</template>

<script>
    export default {
        data () {
            return {
                message: 'Hello World'
            }
        }
    }
</script>

import TopBar from './top-bar.vue'

<top-bar></top-bar>

Vue.component('top-bar', TopBar);

<template>
    <top-bar></top-bar>
    <div class="message">{{ message }}</div>
</template>

<script>
    import TopBar from './top-bar.vue'
    export default {
        data () {
            return {
                message: 'Hello World'
            }
        },
        components: {
            TopBar
        }
    }
</script>