JSFiddle - React, Tailwind, and code Playground

HTML

<script>
function myFunction(){
    var x = document.getElementById("input1");
    var y = document.getElementById("input2");
    y.value=x.value;
}    
    </script>
Input 1: <input type="text" id="input1" onkeydown="myFunction()"/>
Input 2: <input type="text" id="input2"/>