From what I’ve picked up so far, Wallaby.js works in a fairly similar way to NCrunch; it has a change detection algorithm that tries to map changes in tracked files to tests that might be affected, and runs these at every opportunity. I’m using VS Code as an editor, and that gives green/red dots in the margin, showing coverage, and there are some very cool integration features. There’s a little server built in, with a web based interface to show the test status – I guess that would be more use in a less powerful editor. What’s really nice though is that test failures have hyperlinks – in the console output and in the browser, which redirect the editor straight to the affected area.
Probably my favorite thing so far is the inline display of console log information – just by dropping in a console log, a pretty-printed representation of any object is shown over the code. This gives a really fast feedback loop without resorting to debugging – it’s early days, but seems well worth a try!