An Apollo Server formatError function that avoids "Converting circular structure to JSON" errors

graphql-apollo-xray-error-formatter.js

// This is the attribute that continuation local storage uses to hold onto
// the current context. The value comes from https://github.com/othiym23/node-continuation-local-storage/blob/fc770288979f6050e4371c1e1b44d2b76b233664/context.js#L11
const CLS_CONTEXT_ATTRIBUTE = 'error@context';

// A formatError function that can be used with
//   https://www.apollographql.com/docs/apollo-server/features/errors#for-the-client-response
function formatError (err) {
  // The continuation-local-storage module attaches a context attribute to
  // errors so that the context can be resolved from errors. The attribute
  // is enumerable by default and so it gets included in GraphQL error
  // reporing. That alone would not be a problem, but AWS X-Ray's context
  // holds a reference to the error leading to an object with circular
  // references. Apollo Server does not handle circular references
  // gracefully: https://github.com/apollographql/apollo-server/issues/1433
  // This workaround marks the CLS context as not enumerable, which means
  // not serialized by JSON.stringify(), which means is will not trigger the
  // Apollo bug
  const originalException = err.extensions && err.extensions.exception;
  if (originalException && CLS_CONTEXT_ATTRIBUTE in originalException) {
    Object.defineProperty(originalException, CLS_CONTEXT_ATTRIBUTE, {
      enumerable: false;
    });
  }
  return err;
}

Minor comment but you've got an invalid semicolon on line 21.