SOURCE

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>
  <button v-on:click="reverseMessage">
  Reverse Message
  </button>
</div>