Adding a javascript target to check compatibility.

**Describe the feature request**
We would like to support members of the javascript community.

**Additional context**
We need to add a run of all tests in CI to find out if we are working correctly on this platform.

Start by locating the repository's CI configuration and the existing full test runs, then check how other platform targets are defined. Done means CI runs all tests against a JavaScript target and reports whether Cabal works correctly for that platform.

Written by the indexing model from the issue text.