JSFiddle - React, Tailwind, and code Playground

HTML

<p>A function is triggered when the user releases a key in the input field. The function transforms the character to upper case.</p>
Enter your name: <input type="text" id="fname" onkeyup="myFunction()">

JavaScript

function myFunction() {
    var x = document.getElementById("fname");
    x.value = x.value.toUpperCase();
}