code: function(id) {
              var size = options.getSize(id),
                  name = options.getName(id);
  
              log("All chunks have been uploaded for " + id + " - finalizing....");
              handler.finalizeChunks(id).then(
                  function(response, xhr) {
                      log("Finalize successful for " + id);
  
                      var normaizedResponse = upload.normalizeResponse(response, true);
  
                      options.onProgress(id, name, size, size);
                      handler._maybeDeletePersistedChunkData(id);
                      upload.cleanup(id, normaizedResponse, xhr);
                  },
                  function(response, xhr) {
                      var normalizedResponse = upload.normalizeResponse(response, false);
  
                      log("Problem finalizing chunks for file ID " + id + " - " + normalizedResponse.error, "error");
  
                      if (
                          normalizedResponse.reset ||
                          (xhr && options.chunking.success.resetOnStatus.indexOf(xhr.status) >= 0)
                      ) {
                          chunked.reset(id);
                      }
  
                      if (!options.onAutoRetry(id, name, normalizedResponse, xhr)) {
                          upload.cleanup(id, normalizedResponse, xhr);
                      }
                  }
              );
          }
docs: Called when all chunks have been successfully uploaded and we want to ask the handler to perform any logic associated with closing out the file, such as combining the chunks.