Trigger page load events in Google Analytics with JavaScript when using Google Tag Manager

gtm-ga-virtual-page-load.js

if (typeof ga === "function") {
  ga.getAll().forEach((tracker) => {
    tracker.set('page', '/my/path'); // <- change here
    tracker.send('pageview');
  });  
}

// ES5 version for backward compatibility
if (typeof ga === "function") {
  ga.getAll().forEach(function (tracker) {
    tracker.set('page', '/my/path'); // <- change here
    tracker.send('pageview');
  });  
}

Google Tag Manager is both amazing and awful. The official solution for sending virtual page loads is to set up a custom event in the Tag Manager UI with a page variable, and then trigger this event with datalayer.push(). I don't like the added complexity of setting up a custom event if I don't have to. There's also the risk that it could get broken at any time by someone (me) who messes around in the Tag Manager UI.

This solution is basically the same as when using the good old analytics.js. What you need to do differently with Tag Manager is that you have to get the tracker object dynamically, as explained by Simo Ahava in this thread.