How do I create a popup?

I've used the following Java Script for years on several sites, to great satisfaction. I tried to set it up on my SquareSpace site, but it doesn't seem to be working:

For it to work, additional elements need to be added to the link, i.e. "javascript:popupWindow('...')", which I was able to add to the html script.... but it's still not working. See here for two examples:
https://emfbioshield.squarespace.com/livres/ and here: https://emfbioshield.squarespace.com/videos/

Any idea why it's not working?

Thanks for any help!