I understood what pjax was doing in about 5 minutes. Backbone.js is more complicated than that, and while I'm certain it's not that hard to figure out, I felt a bit like "ok, it's doing stuff I don't immediately understand, but it's also not doing any deep magic that makes difficult things super-easy, either". Very subjective, but it just didn't feel like a sweet spot. Angular.js actually seemed like more of an "all-in" play with the fancy stuff, but that datepicker issue was a wake up call about getting to a point where even doing something simple might be quite difficult.