Vue

HTML

<div id="app">
  <button @click="inc">+ 1 day</button>
  <button @click="dec">- 1 day</button>
  <br /><br />

  {{date}}
</div>

CSS

body {
  background: #20262E;
  padding: 20px;
  font-family: Helvetica;
}

#app {
  background: #fff;
  border-radius: 4px;
  padding: 20px;
  transition: all 0.2s;
}

li {
  margin: 8px 0;
}

h2 {
  font-weight: bold;
  margin-bottom: 15px;
}

del {
  color: rgba(0, 0, 0, 0.3);
}

Vue

new Vue({
  el: "#app",
  data: {
    date: new Date()
  },
  methods: {
  	inc () {
    	this.date.setDate(this.date.getDate() + 1)
      this.date = new Date(this.date)
      console.log(this.date)
		},
    dec () {
    	this.date.setDate(this.date.getDate() - 1)
      this.date = new Date(this.date)
      console.log(this.date)
    }
  }
})