async function searchDocuments() {
    // Initialize request argument(s)
    const searchRequest = {
      // The full resource name of the location, e.g.:
      // projects/{project_number}/locations/{location}
      parent: `projects/${projectNumber}/locations/${location}`,

      // Document Text Query
      documentQuery: {
        query: documentQueryText,
        // File Type Filter
        fileTypeFilter: {
          fileType: 'DOCUMENT',
        },
      },

      // Histogram Query
      histogramQueries: [
        {
          histogramQuery: 'count("DocumentSchemaId")',
        },
      ],
      requestMetadata: {userInfo: {id: userId}},
    };

    // Make Request
    const response = serviceClient.searchDocuments(searchRequest);

    // Print out response
    response.then(
      result => console.log(`Document Found: ${JSON.stringify(result)}`),
      error => console.log(`${error}`)
    );
  }
TODO(developer): Uncomment these variables before running the sample.
const projectNumber = 'YOUR_PROJECT_NUMBER';
const location = 'YOUR_PROJECT_LOCATION'; // Format is 'us' or 'eu'
const userId = 'user:xxx@example.com'; // Format is "user:xxx@example.com"
const documentQueryText = 'YOUR_DOCUMENT_QUERY'