access vue data component

i created a simple component but when i try to access data component it returns undefined here is my code:

Vue.component({
  template:`<div>{{message}}</div>`,
  data() {
     return { comments: [
        {title: 'hello' , message: 'world'},
        {title: 'hellowww' , message: 'worldssss'},
     ]}
  },
  mounted: function() {
      console.log(this.comments) // undefined. dosnt work
      console.log(this.$root.comments) //undefined. dosnt work
      console.log(comments) //undefined. dosnt work
  }

});

var app = new Vue({
   el: '#root'
});