Error handling consistency/conventions

I ran into this a while back and never raised it, but since I’m here and contributing to the error handling code (#128 #126 #118) I thought I’d bring it up now.

Errors should be instanceof Error

I would have expected the errors provided in the catch(err) callback to have been instanceof Error, as is suggested by the MDN docs for Promise.reject(reason):

For debugging purposes and selective error catching, it is useful to make reason an instanceof Error.

Indeed the convention for the continuation-style callback passing cb(err) is widely recognised, supported and provided by module authors (supporting material: 1,2).

Error handling should be consistent

In debugging and fixing #126, I discovered different error handling strategies for:

• download request
• RPC request
• upload request

The difference being that the error response json is parsed in the RPC request, but not the others. I believe that this inconsistency was introduced by accident rather than design (in the fix to #108).

Solution

I think the solution should be to extract the error construction into a common function that is used by each request type. This will ensure consistency between request type.

The error constructed should be an Error object, and I see no reason why the information that is attached to the current non-Error object format could not be attached.

For example (just a quick sketch, not an exhaustive solution), something like:

var buildCustomError = function (error, response) {
  var msg;
  if (response) {
    try {
      msg = JSON.parse(response.text).error_summary;
    } catch (e) {
      msg = error.message;
    }
  }
  var err = new Error(msg);
  err.status = error.status;
  err.response = response;
  return err;
};

Let me know what you think. I’d be happy to put together a PR that implements this solution, or leave it with you to implement. Cheers.

[good-lly]

would be very nice to see error handling in some /example

[greg-db]

We’ve updated the error handling in release v8.0.0, and added a note to the Upgrading document. Please upgrade to the latest version and let us know if you’re still seeing any issues. Thanks!