add opt-in global error-handling (by default)

this gets redundant on the client:

  request
  .get('/querystring')
  .query('search=Manny')
  .query({ order: 'desc', range: '1..5' })
  .end(function(res){
    if (res.error) return something(res.error)
  });

ideally you opt in with something similar to:

request.on('error', function(err){

});

though this would be a bit of a hack since we have no .error(fn) to opt-into http errors in the first place. Arguably global handling is an anti-pattern but worth thinking about

[apsavin]

An example of quick and dirty workaround:

const end = superagent.Request.prototype.end;
superagent.Request.prototype.end = function (callback) {
  return end.call(this, (error, response) => {
    if (response.unauthorized) {
      // handle the error here, for example:
      // window.location = '/login'
    } else {
      callback(error, response);
    }
  });
};

[boucher]

I believe .end is not supported by superagent-defaults.