Converting an image to base64 encode from its url

convert-img-to-base64.js

// from a component controller
toDataURL(
  image_url
).then(
  function onsuccess(response) {
    ctrl.ngModel.$setViewValue(ctrl.previousImage);
  },
  function onError(response) {
    $log.error(response);
  }
);

function createRequest(method, url) {
  var xhr = new XMLHttpRequest();
  if ('withCredentials' in xhr) {
    // XHR for Chrome/Firefox/Opera/Safari.
    xhr.open(method, url, true);
  } else if (typeof XDomainRequest != 'undefined') {
    // XDomainRequest for IE.
    xhr = new XDomainRequest();
    xhr.open(method, url);
  } else {
    // CORS not supported.
    xhr = null;
  }
  return xhr;
}
function toDataURL(url) {
  // build a promise
  var _deferred = $q.defer();
  if ($window.FileReader){
    var xhr = createRequest('GET', url);
    xhr.onload = function() {
      var reader = new FileReader();
      reader.onloadend = function onLoadData(event) {
        _deferred.resolve(event.target.result);
      }
      // after get the data transfor it to base64
      reader.readAsDataURL(xhr.response);
    };
    xhr.open('GET', url, true);
    xhr.responseType = 'blob';
    xhr.send();
  }
  else {
    _deferred.reject('The client browser do not support FileReader()');
  }
  return _deferred.promise;
}