SRT to WebVTT in Javascript

srtToVtt.js

(function () {

  window.srtToVtt = function (url, cb) {
    var xhr = new XMLHttpRequest();

    xhr.onload = function () {

      var vtt = 'WEBVTT FILE\r\n\r\n';
      var blob;
      var url;

      if (xhr.readyState !== xhr.DONE) {
        return;
      }

      vtt += xhr.responseText;

      // replace bracket tags with html tags
      vtt = vtt.replace(/\{(\/?[biu])}/g, '<$1>');

      // vtt uses a dot between seconds and milliseconds
      vtt = vtt.replace(/(\d\d:\d\d:\d\d),(\d\d\d)/g, '$1.$2');

      blob = new Blob([vtt], {type: 'text/vtt; charset=UTF-8'});
      url = URL.createObjectURL(blob);

      cb(url);
    };

    xhr.open('GET', url);
    xhr.send();
  }

}());

srtToVtt('captions.srt', function (url) {
  // use url as text track
});