code: function(mimeType, quality) {
              try {
                  // If this call fails (due to browser bug, like in Firefox 3.6),
                  // then revert to previous no-parameter image/png behavior
                  return this._canvas.toDataURL(mimeType, quality);
              }
              catch(e) {
                  try {
                      return this._canvas.toDataURL();
                  }
                  catch(err) {
                      Kinetic.Util.warn('Unable to get data URL. ' + err.message);
                      return '';
                  }
              }
          }
docs: to data url
  @method
  @memberof Kinetic.Canvas.prototype
  @param {String} mimeType
  @param {Number} quality between 0 and 1 for jpg mime types
  @returns {String} data url string