code: function checkFileReaderSyncSupport() {
          var worker = makeWorker(syncDetectionScript);
          if (worker) {
              worker.onmessage =function(e) {
                  FileReaderSyncSupport = e.data;
              };
              worker.postMessage({});
          }
      }
docs: checkFileReaderSyncSupport: Create a temporary worker and see if FileReaderSync exists