Yet another JS code coverage tool that computes statement, line, function and branch coverage with module loader hooks to transparently add coverage when running tests. Supports all JS coverage use cases including unit tests, server side functional tests and browser tests. Built for scale.
Seems like there are a lot of bugs with Istanbul + ES2015. One of them is that you can't use the export statements as you should with ES2015.
Most of the time Istanbul dies silently, or throw errors.
I gave details about it here: https://github.com/Kflash/farris#known-bugs. See the section about Istanbul.