Creating a downloadable text-file using blobs with automatic download start

Created as part of my answer to http://stackoverflow.com/questions/8178825/create-text-file-in-javascript

HTML

<button id="create">Create file</button>

JavaScript

(function () {
var oldUrl = null,
  makeObjectUrl = function (value) {
    var data = new Blob([value], {type: 'application/pdf'});

    // If we are replacing a previously generated file we need to
    // manually revoke the object URL to avoid memory leaks.
    if (oldUrl !== null) {
      window.URL.revokeObjectURL(oldUrl);
    }

    oldUrl = URL.createObjectURL(data);

    return oldUrl;
  };


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

  create.addEventListener('click', function () {
    var pdfData =...