Express-promise-handler NPM

express-promise-handler

Allows express middlewares to return promise by wrapping the middlewares.

Makes express route handlers testable by avoiding use of res.
Slightly easier to work with promises.

Objective

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

Concepts

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 choose 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

3.3.1 2023-12-23

Fix the type check for HTTPError using instanceof instead of constructor name. It was causing issues when used with got where the error is also named HTTPError.