Cannot use relative URL for the baseURL option

[rschristian]

(Using Preact-CLI's issue template as I find it easy to read)

Do you want to request a feature or report a bug?

Likely a bug

What is the current behavior?

Currently Redaxios cannot use relative URLs for its baseURL. The URL() constructor, if passed a base parameter, needs that parameter to be a valid URL on its own, and a relative URL like /api/ is not. MDN Docs.

If the current behaviour is a bug, please provide the steps to reproduce.

Simply open a browser console and write:

new URL('foo', '/api/');

You will get an error stating the following:

Uncaught TypeError: URL constructor: /foo/ is not a valid URL.

That example is how Redaxios currently forms its URLs when a baseURL is supplied

What is the expected behaviour?

I'd like to be able to use relative URLs for the base as they're very handy for proxying front-end applications.

[mfix22]

If it helps, this PR reproduces the issue: carbon-app/carbon#1054 (just open the "Background Image" menu w/ a debug point set in the redaxios try/catch)