Express Middleware for Bunyan logging

index.js

var bunyan = require('bunyan');

module.exports.logger = function logger(log) {
  if (typeof (log) !== 'object')
    throw new TypeError('log (Object) required');

  this.log = log;

  var self = this;
  return function logger(req, res, next) {
    req.log = log;
    self.log.info({req: bunyan.stdSerializers.req(req)}, 'start');
    next();
  };
};

module.exports.errorLogger = function(log) {
  if (typeof (log) !== 'object')
    throw new TypeError('log (Object) required');

  this.log = log;

  var self = this;
  return function logger(err, req, res, next) {
    if (err)
      self.log.trace({err: err}, 'error');
    next();
  };
};

The use of this looks dangerous. These are not constructors, so this refers to the scope of the module, allowing strange behaviour with collisions. There doesn't appear to be any need to use this, as the scope should take care of itself:

var bunyan = require('bunyan');

module.exports.logger = function logger(log) {
  if (typeof log !== 'object') {
    throw new TypeError('log (Object) required');
  }

  return function logger(req, res, next) {
    req.log = log;
    log.info({ req: bunyan.stdSerializers.req(req) }, 'start');
    next();
  };
};

module.exports.errorLogger = function(log) {
  if (typeof log !== 'object') {
    throw new TypeError('log (Object) required');
  }

  return function logger(err, req, res, next) {
    if (err) {
      log.trace({ err: err }, 'error');
    }

    next();
  };
};