<div id="app">
  <div>
    <button @click="incrementCount">Click me!</button>
    <p>Count: {{ countDisplay }}</p>
  </div>  
<div>
new Vue({
  data(){
    return {
      count: 0
    }
  },
  computed: {
    countDisplay(){
      return `Count: ${this.count}`
    }
  },
  el: "#app",
  methods: {
    incrementCount(){
      this.count += 1
    }
  },
  watch:{
    count(newVal){
      console.info(`Count updated to ${newVal}`)
    }
  }
})

External CSS

This Pen doesn't use any external CSS resources.

External JavaScript

  1. https://cdnjs.cloudflare.com/ajax/libs/vue/2.7.8/vue.min.js