However, "instantly smooth transitions" may not require using JavaScript. According to the blog post, GitLab observed a performance increase after ditching Turbolinks[1]. Indeed, sites that use JS to speed up page loads are often compensating for what would otherwise be an excessively slow load, due to having lots of scripts or whatnot. And that's only a partial fix: the user still experiences that slow load whenever they come in from an external site or open links in a new tab/window. If you can make "real" page loads fast, you avoid that problem.
[1] ...though it doesn't seem to have been measured very scientifically - to quote from the pull request: "I thought I noticed that pageloads were a lot more snappy, and one other reviewer said the same. Not the most rigorous way to test performance, but it helps."
Sometimes I feel like 95% of the thrashing in the JS world is from people trying to fix the wounds inflicted by the previous Hot New Thing...
Right now, GitLab is fast and snappy for people that self-host it, but GitLab.com is not and we're not happy with that [0]. Making our front end performant is part of that and I'm happy our engineers have been working hard on that.
We have been using Prometheus extensively to monitor speed of transactions on the backend and I'm seeing a strong push to more monitoring to front end monitoring as well (I owe you a link here).
The performance issues we plan to work on are in https://gitlab.com/gitlab-org/gitlab-ce/issues?scope=all&utf...