I want to get a base64-String from an firebase hostet image-URL. It's working well on all Browsers, but not when I'm building an iOS or Android App with ionic.

getDataUrl(url) {
    return new Promise(function (resolve, reject) {
      var request = new XMLHttpRequest();
      request.open('GET', url, true);
      request.responseType = 'blob';
      request.onload = function () {
        var reader = new FileReader();
        reader.readAsDataURL(request.response);
        reader.onload = function (e) {
          console.log('DataURL:', e.target.result);
          resolve(e.target.result)
        };
        reader.onerror= function (e) {
          console.log('Error:', e.target.error.code);
          reject(e.target.result)
        };
      };
      request.send();
    });
  }

Unfortunately it seems to stop at reader.readAsDataURL(request.response); but there is no logged error to check.