• BigQuery UDFs don't support certain browser APIs like URL due to their restricted JavaScript runtime environment.

• BigQuery UDFs can't call external APIs, it won't be able to run and perform additional API calls. As mentioned by @Mikhhali can try with the BigQuery NET functions .

As of now BigQuery UDFs do not support browser-specific APIs like URL .If you want that feature you can open a new Feature request as per your requirements on the public issue tracker describing your issue and vote [+1] and Eng team will look on the feature for future implementation