JSFiddle - React, Tailwind, and code Playground

HTML

<script src="https://unpkg.com/vue/dist/vue.js"></script>

<div id="app">
  <h1>{{ message | uppercase(false) }}</h1>
</div>

JavaScript

var vm = new Vue({
	el: '#app',
  data: {
    message: 'hello world!'
  },
  filters: {
  	uppercase: function(value, onlyFirstCharacter) {
    	if (!value) {
      	return '';
      }
      
      value = value.toString();
      
      if (onlyFirstCharacter) {
      	return value.charAt(0).toUpperCase() + value.slice(1);
      } else {
      	return value.toUpperCase();
      }
    }
  }
});