This does only one thing, and one thing only.

It exposes a reactive property $online to every component, which you can use like this:

<div v-if="!$online"> 
	Opps! You are offline!
</div>

That's all!

How to install

import VueOnlineProp from "vue-online-prop"
Vue.use(VueOnlineProp)

It's a really tiny plugin (<1kb, unminified).