JSFiddle - React, Tailwind, and code Playground

HTML

<html>
<head>
  <script>
   function onWorkDone(data) {
    alert(data.result);
   }
  </script>
  <script src="callback.js"></script>
</head>
</html>

JavaScript

function doWork(callback) {
  callback({result: 'foo'});
}
doWork(onWorkDone);