JSFiddle - React, Tailwind, and code Playground

HTML

<script>
function readFile() {
  var file    = document.querySelector('input[type=file]').files[0];
  var reader  = new FileReader();

  reader.readAsText(file);
  reader.onload = function(e) {
  var text = reader.result;
  alert(text);
  }
}
</script>
<input type="file" onchange="readFile()"><br>