JSFiddle - React, Tailwind, and code Playground

HTML

<input class="sync-field" type="text">
<div class="sync-target"></div>

JavaScript

var field = document.querySelector('.sync-field'),
		target = document.querySelector('.sync-target');

field.addEventListener('input', function() {
	
  var val = this.value;
  
	val = val.replace(/a/g, 'A');  // latin
  val = val.replace(/а/g, 'А');  // cyrillic
  
  target.textContent = val;

});