The JS SDK for sync is in progress: https://github.com/wtrocki/offline-conflict-strategies

There's an app currently which will eventually become the sdk: https://github.com/wtrocki/offline-conflict-strategies

What has to be done for this task is get the device/app info and pass it as headers.

Getting the device/app info:
https://github.com/aerogear/aerogear-js-sdk/blob/f9783a4ce192f4653a1668aee5fb7c2ebcf69f9f/packages/core/src/metrics/platform/CordovaDeviceMetrics.ts
and
https://github.com/aerogear/aerogear-js-sdk/blob/f9783a4ce192f4653a1668aee5fb7c2ebcf69f9f/packages/core/src/metrics/platform/CordovaAppMetrics.ts

Note: clientId has to be sent as well: https://github.com/aerogear/aerogear-js-sdk/blob/f9783a4ce192f4653a1668aee5fb7c2ebcf69f9f/packages/core/src/metrics/MetricsService.ts#L103

Passing headers to sync requests:
https://github.com/wtrocki/offline-conflict-strategies/blob/da016ec84771c3ea71e8e5af3a20144e11b97eb2/web/src/apolloClient.js#L27

   const httpLink = new HttpLink({

      uri: uri || '/graphql',

      fetch,

      fetchOptions: fetchOptions || {},

      credentials: credentials || 'same-origin',

      headers: headers || {},

    });

This one will wait until the JS SDK for sync is moved to proper place.