Can't launch repos in mybinder.org UI: Uncaught TypeError: URL constructor: /build/gh/binder-examples/conda/HEAD is not a valid URL.

[manics]

Bug description

I had to revert jupyterhub/mybinder.org-deploy#2746 (which includes #1741) as it causes a Javascript error on the main mybinder.org page. This seems to prevent launching any repository.

How to reproduce

The occurred after entering https://github.com/binder-examples/conda into mybinder.org (deployment has since been reverted and is working again). It failed to launch, and this error was in the browser console:

Uncaught TypeError: URL constructor: /build/gh/binder-examples/conda/HEAD is not a valid URL.

The browser debugger indicated

binderhub/js/packages/binderhub-client/lib/index.js

Line 28 in 527ac45

let apiUrl = new URL(this.baseUrl + "build/" + this.providerSpec);

is the source

Note this is not reproducible using the test configurations in https://github.com/jupyterhub/binderhub/tree/main/testing

[yuvipanda]

Sorry about missing this @manics. I've now opened #1758, which starts adding JS unit tests here as well. There's going to be a bit of work needed before the unit tests can 'fully' catch things, but it's a start.

[yuvipanda]

This has since been fixed