Focusing a form element on page load

I’m trying to get the first field in my form to automatically focus when the page loads. I’ve not found a tick box for this, so I’ve tried to do it by going to app properties and creating a dynamic event for when my app loads to set the focus on the element. This doesn’t seem to work though, so to test it I tried to show a browser alert on page load but this doesn’t seem to be working either.

Have I missed a key step out here to get this working?

Many thanks,

Neil