What is the best non-functional testing tool for a website built almost entirely using Java/JavaScript/AngularJS?

I've been trying to perform load and stress tests on a webpage built almost entirely using Java/JavaScript/AngularJS using JMeter, and while it performs some of the tasks I need, I'd like to be able to run the JS responses the webpage sends, for example. There's also an issue of being able to extract the values of some variables that appear only in name, but whose value is never explicitly stated, in the various scripts that a few of the HTTP requests contain, that is proving hard to perform suitably in JMeter. What would be a better tool, or way to go about performing these tests?