SOURCE

var vm = new Vue({
    el: '#app',
    data:{
      typewriter: '',
      i: 0,
      timer: 0,
      str: 'Hi,this is a test.'
    },
    mounted () {
        this.typeing()
    },
    methods: {
        typeing () {
            if (this.i <= this.str.length) {
                this.typewriter = this.str.slice(0, this.i++)
                this.timer = setTimeout(() => {
                    this.typeing()
                }, 200)
            } else {
                clearTimeout(this.timer)
            }
        }
    }
});

<div id="app">
  <p class="typewriter">{{ typewriter }}</p>
</div>

#app {
  font-family: Avenir, Helvetica, Arial, sans-serif;
  -webkit-font-smoothing: antialiased;
  -moz-osx-font-smoothing: grayscale;
  text-align: center;
  color: #2c3e50;
  margin-top: 60px;
}