Wallaby.js is a continuous test runner that outputs results directly into your editor. It includes code coverage, so you'll get a visual indication of blocks of code that aren't tested. It also uses dependency analysis to only run tests affected by changes, and runs tests in parallel to improve performance.
The supported editors include:
The authors are working on Visual Studio support as well.
The following screenshot shows the line covering test feature:
There's an example project that you can use to see how Wallaby works in practice.
The project is commercial but is currently free to try out. Wallaby's creator, Artem Govorov, has written a blog post about the motivation behind starting the project.
This allows us to serve more simultaneous requests, increasing the performance of the application. As a result, we can serve multiple variants of the page without needing to rely on HTTP caches such as Varnish; we cache each module on the page in Redis and construct the page using the cached fragments instead.
When I was working on Node.js in Practice, the development team at the publisher kept pushing us to prove why Node is fast. They were concerned that it was all hyperbole, so we were constantly challenged to argue our performance assertions. I was encouraged to read that the programmers at the BBC have found Node to perform well enough for their large scale site, so if this project goes well it'll be a great testimonial for Node.
Andrew also mentions that they've used React and Browserify. I've increasingly found Browserify to be the right choice for front-end work: