Google Gloud Vision API - Return Output as JSON Object rather than to a GCS file

I am utilising the Cloud Vision API "PDF to Text" function for a Node.js app. I have mostly stuck close to the GCP docs example, with a couple of tweaks here and there: https://cloud.google.com/vision/docs/pdf

All works fine, however I would like the contents of the file to be returned to me as a JSON object so I can pass it into another funciton, rather than its current behaviour of writing the contents to a JSON file and storing it on Cloud Storage.

Does anyone know how I need to structure the outputConfig object in order to achieve this?

async function detectPdfText(bucketName, fileName) {
    // Imports the Google Cloud client libraries
    const vision = require('@google-cloud/vision').v1;

    // Creates a client
    const client = new vision.ImageAnnotatorClient({
        keyFilename: './APIKey.json'
    });

    // The directory to store the results
    const outputPrefix = 'json_output'

    const gcsSourceUri = `gs://${bucketName}/${fileName}`;
    const gcsDestinationUri = `gs://${bucketName}/${outputPrefix}/`;

    const inputConfig = {
        // Supported mime_types are: 'application/pdf' and 'image/tiff'
        mimeType: 'application/pdf',
        gcsSource: {
            uri: gcsSourceUri,
        },
    };
    const outputConfig = {
        gcsDestination: {
            uri: gcsDestinationUri,
        },
    };
    const features = [{type: 'DOCUMENT_TEXT_DETECTION'}];
    const request = {
    requests: [
        {
            inputConfig: inputConfig,
            features: features,
            outputConfig: outputConfig,
        },
    ],
    };

    const [operation] = await client.asyncBatchAnnotateFiles(request);
    const [filesResponse] = await operation.promise();
    const destinationUri =
        filesResponse.responses[0].outputConfig.gcsDestination.uri;
    console.log(`Json output for file ${fileName} has been saved to: ${destinationUri}`);
}

module.exports = { detectPdfText };