How to preview partial job results in JavaScript SDK?

[omerl]

Hey!
I'm trying to run a search in the JS Splunk SDK, and periodically check the job for the current results. I found out that there are multiple exec_modes possible, and if I set it to normal, I can get the job ID before the search has ended.
I tried to run my job this way:

service.search(
  searchQuery,
  searchParams,
  async function (err, job) {
    console.log("...done!\n");
    let count = 0;
    const sleep = ms => new Promise(resolve => setTimeout(resolve, ms))
    await sleep(4000);
    job.preview({}, function (err, results) {
      if (err) {
        console.error(err)
        return;
      }
      if (results.rows) {
        count++;
        console.log("========== Iteration " + count + " ==========");
        console.log(results.rows)
        for (var i = 0; i < results.rows.length; i++) {
          var row = results.rows[i];
          console.log(stat + row[countIndex]);
        }
        console.log("=================================");
      }
    });
});

with these properties:

const searchQuery = "search index=*";
const searchParams = {
  exec_mode: "normal"
};

The output of this job.preview is that there are no rows yet.

Is there anything wrong with the way I'm checking the job results? Is there a way to achieve the results before the job ends?

Thanks!