Modern Day Xajax Replacement For Front End


Hello everyone,,
We have a large(~500k lines of code) custom built system we run a business on. Many of it's larger sub-systems front ends(Points of sales, etc.) are built around the PHP library Xajax. Xajax still is working "ok" for us even on PHP 7.3, however that project is no longer maintained and at this point I believe it's "dead". I've seen the project Jaxon that appears to be a fork of it, but I'm not sure how long that will be around, how popular it is, etc.(haven't tried it)

I'm looking to make the best decision possible for what we replace Xajax with moving forward. We would ultimately slowly re-do some of our subsystems using the new library / tools we decide on as well as new ones we create.

We aren't running on a popular framework and have no plans to move to one. We also currently are using smarty templates for our templating engine.

I've looked at doing ajax through jquery, and although it can be done, it looks like it would be much more verbose and code heavy than what we are doing today with xajax.

My gut tells me that angular, or vue.js hitting an API for pulling and manipulating data is possibly one of the better directions to go? Thoughts?