JSFiddle - React, Tailwind, and code Playground

HTML

<input type="file" id="openselect" />
<textarea id="showresult"></textarea>

CSS

#showresult {
  width: 98%;
  height: 200px;
}

JavaScript

function doOpen(evt) {
  var files = evt.target.files,
    reader = new FileReader();
  reader.addEventListener("load", function() {
    showout.value = this.result;
  });
  reader.readAsText(files[0]);
}

var openbtn = document.getElementById("openselect"),
  showout = document.getElementById("showresult");
openselect.addEventListener("change", doOpen, false);