SOURCE

var app = new Vue({
  el: '#app',
  data: {
     message: 'Hello Vue.js!'
  },
   methods: {
    reverseMessage: function () {
      this.message = this.message.split('').reverse().join('')
    }
  }
})

<div id="app">
  <p>{{ message }}</p>
  <input v-model="message">
</div>