Passing in Async functions to Node.js Express.js router

Question

This seems like a straightforward google, but I can\'t seem to find the answer...

Can you pass in ES7 async functions to the Express router?

Example:

<         


        

Answer 1

Use express-promise-router.

const express = require('express');
const Router = require('express-promise-router');
const router = new Router();   
const mysql = require('mysql2');

const pool = mysql.createPool({
  host: 'localhost',
  user: 'myusername',
  password: 'mypassword',
  database: 'mydb',
  waitForConnections: true,
  connectionLimit: 10,
  queueLimit: 0
}).promise();

router.get('/some_path', async function(req, res, next) {
  const [rows, ] = await pool.execute(
    'SELECT * ' +
    'FROM mytable ',
    []
  );

  res.json(rows);
});

module.exports = router;

(The above is an example of using mysql2's promise interface with express-promise-router.)

Answer 2

I think you can't do it directly because exceptions are not caught and the function won't return if one is thrown. This article explains how to create a wrapper function to make it work: http://thecodebarbarian.com/using-async-await-with-mocha-express-and-mongoose.html

I haven't tried it but was investigating this recently.

Answer 3

It sort of works, but not really

While it seems to work, it stops handling errors thrown inside the async function, and as a result, if an error is not handled, the server never responds and the client keeps waiting until it timeout.

The correct behavior should be to respond with a 500 status code.

---

Solutions

express-promise-router

const router = require('express-promise-router')();

// Use it like a normal router, it will handle async functions

express-asyncify

const asyncify = require('express-asyncify')

To fix routes set in the app object

Replace var app = express(); with

var app = asyncify(express());

To fix routes set in router objects

Replace var router = express.Router(); with

var router = asyncify(express.Router());

Note

You only need to apply the asyncify function in the objects where you set the routes directly

https://www.npmjs.com/package/express-asyncify

Answer 4

May be you didn't found results because async/await is an ES7 not ES6 feature, it is available in node >= 7.6.

Your code will work in node. I have tested the following code

var express = require('express');
var app = express();

async function wait (ms) {
  return new Promise((resolve, reject) => {
    setTimeout(resolve, ms)
  });
}

app.get('/', async function(req, res){
  console.log('before wait', new Date());
  await wait(5 * 1000);
  console.log('after wait', new Date())
  res.send('hello world');
});

app.listen(3000, err => console.log(err ? "Error listening" : "Listening"))

And voila

MacJamal:messialltimegoals dev$ node test.js 
Listening undefined
before wait 2017-06-28T22:32:34.829Z
after wait 2017-06-28T22:32:39.852Z
^C

Basicaly you got it, you have to async a function in order to await on a promise inside its code. This is not supported in node LTS v6, so may be use babel to transpile code. Hope this helps.

Answer 5

To handle async requests in express routes use a try catch, which helps you to try for any errors in function and catch them. try{await stuff} catch{err}