express-promise-handler

allows express middlewares to return promise by wrapping the middlewares

Objective

Make the express route controllers easy to test and easy to read

Concepts

Exported object

module.exports = {
  default: (function(req:object):any) => {
    return function(req:object, res:object)
  },
  HTTPError: class HTTPError extends Error
}

• return from the callback is sent as response
• object based responses are returned as json
• thrown errors are caught and handled with 500
• custom error can be thrown using HTTPError
• returning undefined will call the next method. If there is no next, this can result in 504 timeout.

Example

Setting up routes

let ContentController = require('./content.controller');
let Router = require('express').Router;
let controller = new ContentController();
let router = new Router();

let promiseHandler = require('express-promise-handler').default;

router.get('/:id', promiseHandler(controller.info));

module.exports = router;

In the controller

const HTTPError = require('express-promise-handler').HTTPError;

class ContentController {
  info(req) {
    return models.content.findOne({
      where: {
        id: req.params.id
      }
    })
    .then((entry) => {
      if (!entry) {
        throw new HTTPError(404, 'entry not found');
      }
      return entry;
    });
  }
}

exports.default = ContentController;

Sample response

{
  "message": "entry not found"
}

{
  "message": "Internal server error: cbnvdtbz51v9pc8h395qd"
}

Error tracking

Thrown errors which are not instances of HTTPError are logged with full stack traces. These stack traces are assigned a unique alphanumeric string which is also sent as part of the response. API clients can chose to display this string to the users in order to track individual issues.

This also ensures that uncaught errors will not have any details conveyed in the response.

Changelog

[2.1.0] - 2017-12-23

Changed

• added feature to handle buffer data as raw

[2.0.0] - 2017-09-24

Changed

• Error in now always json
• HTTPError is considered caught and not logged in detail
• HTTPError.message is now a json object
• handle next() methods in middleware

Alternative:

• express-promise-router

wrapper for Express 4's Router that allows middleware to return promises