JSFiddle - React, Tailwind, and code Playground

HTML

<textarea id="textbox" style="width: 300px; height: 200px;">
To: User <[email protected]>
Subject: Subject
X-Unsent: 1
Content-Type: text/html

<html>
<body>
Test message
</body>
</html>
</textarea> 
<button id="create">Create file</button> 
<a download="message.eml" id="downloadlink" style="display: none">Download</a>

JavaScript

(function () {
var textFile = null,
  makeTextFile = function (text) {
    var data = new Blob([text], {type: 'text/plain'});

    if (textFile !== null) {
      window.URL.revokeObjectURL(textFile);
    }

    textFile = window.URL.createObjectURL(data);

    return textFile;
  };


  var create = document.getElementById('create'),
    textbox = document.getElementById('textbox');

  create.addEventListener('click', function () {
    var link = document.getElementById('downloadlink');
    link.href = makeTextFile(textbox.value);
    link.style.display = 'block';
  }, false);
})();