How does one use async code in sync code when a wrapping class requires values therin?

Question

I am trying to use TypeScript to generate a batch processing job that processes a number of files from Google Cloud Storage and maps a set of workers to batches therin.

I am using the @google-cloud/storage package to read files and generate a set of batches based on file ID i.e.

function getBatches(
    storage:gcs.Storage, 
    bucketName:string, 
    batchSize:number,
    maxBatches:number,
  ):void {
    // Lists files in the bucket
   storage.bucket(bucketName).getFiles().then(files => {
        ... omitted for brevity
        batches = _.slice(batches, 0, maxBatches);
        // how to return?
    }).catch(console.error); 
}

The problem here is that the wrapping class that I use to create the deployment strategy requires that the state be present on run completion i.e.

export class StorageWorkers ... {
     this.jobs ...
     constructor ... {
         ...
         const batches = getBatches(...);
         for (x of batches) {
            this.jobs[x] = new worker.Deployment(x,...); // requires sync 
         };
         // state should be set
     };
};

The problem here is obviously, how could one make getBatches sync such that the output can be used in the subsequent state of the StorageWorkers class?

I have tried implementing the following in the getBatches fn however this tends to return empty on account of async execution.

getBatches(...) ... {
   let outs = [];
   ...then(files => {
        ... omitted for brevity
        batches = _.slice(batches, 0, maxBatches);
        outs.push(batches);
    }).catch(console.error);
   return outs; 
};

I also can't use a callback to set the state for the same reason.

How should one appropriately implement this when a wrapping class uses async code to derive state?