JSFiddle - React, Tailwind, and code Playground

HTML

<label for="password">Password</label>
<input type="password" id="password">
<span id="warning" style="display:none;color:#c00">[Caps Lock]</span>

JavaScript

function capsHandler(event) {
  document.getElementById("warning").style.display = event.getModifierState("CapsLock") ? "inline" : "none";
}
pw = document.getElementById("password");
pw.addEventListener("keyup", capsHandler, false);
pw.addEventListener("focus", capsHandler, false);
pw.addEventListener("click", capsHandler, false);