As with Ruby projects, source code listings have two highlighting modes controlled by the toggle at the top of the listing: the first where quality data is shown as the primary color:
... and the second where coverage data is the primary color:
To report test coverage data to Code Climate, install Code Climate's NPM package and pipe your test coverage data to the provided script (ensuring you set your per-repository repo token):
$ CODECLIMATE_REPO_TOKEN=427acacbc7af8c736b1870edf664822b5737f794a730eda5d646926576e26e15 your-script | codeclimate
Full instructions, including your repository's token can be found by clicking on your repo's settings and then navigating to the Test Coverage section.