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 ES6 ES7 async functions to the Express router?

Example:

var express = require('express'); var app = express();  app.get('/', async function(req, res){   // some await stuff   res.send('hello world'); }); 

If not, can you point me in the right direction on how to handle this problem ES7 style? Or do I just have to use promises?

Thanks!

Answer 1

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 2

Update

Since ExpressJs 5, async functions are supported, and throw errors as expected

Starting with Express 5, route handlers and middleware that return a Promise will call next(value) automatically when they reject or throw an error
source

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In Express 4 or less, 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.

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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