<div id="app">
  <form action="#" @submit="send">
    <input type="text" name="name" v-model="name">
    <input type="text" name="surname" v-model="surname">
    <button>Отправить</button>  
  </form>
  <pre>{{message}}</pre>
</div>

const app = new Vue({
  el: '#app',
  data() {
    return {
      name: '',
      surname: '',
      message: {}
    }
  },
  methods: {
    send (e) {
      e.preventDefault();
      this.message = {
        body: {
          name: this.name,
          surname: this.surname
        }
      }
    }
  }
})