Vue Js String toUpperCase Method

<html>
  <head>
    <script type="importmap">
      {
        "imports": {
          "vue": "https://unpkg.com/vue@3/dist/vue.esm-browser.js"
        }
      }
    </script>
    <body>
     <div id="app">
      <h2>Vue js String toUpperCase Method </h2>
      <button @click="myFunction">click me</button>
      <p>Convert string to Upper case in Vue Js</p>
      <p>Text:{{text}}</p>
      <p>First letter Captital: {{results}}</p>
     </div>
     <script type="module">
      import { createApp } from 'vue'
      createApp({
      data()
      { 
        return{ 
         text:'fontawesomeicons',
         firstLetter:'',
         restLetter:'',
         results:''
        } 
     }, 
     methods:{ 
         myFunction(){ 
            this.firstLetter = this.text.charAt().toUpperCase();
            this.restLetter = this.text.slice(1);
            this.results = this.firstLetter.concat(this.restLetter)
           },
          }
      }).mount('#app')
  </script>

</body>
  </head>
</html>