GTM Custom JavaScript - Set Client ID in a Custom Dimension. Used as a {{Variable}} in a customTask

set-clientid.js

function () {
  return function () {
    try {
      // Retrieve all trackers
      var trackers = ga.getAll();
      trackers.forEach(function(tracker) {
        // Get the Client ID
        var cid = tracker.get('clientId');
        // Set the Client ID in a custom dimension
        tracker.set('dimension1', cid); //change dimension number here
      });
    } catch (e) {}
  }
}