Silent failure when parsing a resonse.body from a 404

Describe the bug

Originally mentioned in https://github.com/purescript-contrib/purescript-affjax/issues/26#issuecomment-768384728

I never was able to figure this out, and ran out of time on the issue for now. It seems like response.body was defined, and looked like this: "{\"errors\":[{\"status\":\"404\",\"title\":\"The resource you are looking for doesn't exist.\"}]}". As I was asking affjax for a string type (and indeed confirmed that this was a string in JavaScript), then parsing it manually. I confirmed that my JSON parser can gracefully fail on that particular string as well, as part of a unit test.

The really interesting this is that in purescript, if I do something like:

  log $ response.body
  log $ response.statusText

The first log will succeed, but execution in that codepath seems to stop after that. The second message is never logged. If I reverse the order of the log statements, the same occurs: the first one logs, the second one does not.

No other errors show up in the web console other than the XHR 404, making it a bit of a mystery there as well.

To Reproduce

Tested with affjax 10.0.0

I haven't yet come up with a self-contained example, but will update here when I do. What is the best way to make some nested widgets in try.purescript.org?

Briefly, my original code looks something like this:

      resEi <- liftAff $ try $ AJ.get AJ.string $ urlToString jsonUrl
      -- ... snip ...
      let res = join $ lmap AJ.XHRError resEi
      in case res of
        Left err -> errorBox $ EX.error $
          "GET /api response failed to decode: " <> AJ.printError err
        Right response -> pure $ Tuple doi (Just $ readRecordJSON response.body)

Adding the log statements after the Right response -> is where things get interesting.

Expected behavior No silent failures - if a failure occurs, an exception should be thrown, or ideally a left value should be generated if possible.

purescript-contrib / purescript-affjax

Silent failure when parsing a resonse.body from a 404 #160