A hack that makes express accept async methods.

example.js

const express = require('express');

const app = express();

app.get(
  '/', 
  async (req, res) => {
    res.json(await something());
  });

app.get(
  '/:user/',
  async (req) => {
    req.user = await User.get(req.params.user);
    if (!req.user) throw new Error('User not found'); // Becomes next(err).
  },
  // Async and non-async can be mixed.
  (req, res) => {
    res.json(req.user);
  }
);

support-async.js

const express = require('express'),
  methods = require('methods'),
  flatten = require('array-flatten');

// We iterate through the router keys.
methods.concat(['use','param','route']).forEach((key) => {

	// Keep the old implementation.
	let old = express.Router[key];

	// Replace with new.
	express.Router[key] = function(...args) {
		
		// Flatten arguments (express does this also).
		args = flatten(args);

		// Map the arguments.
		args = args.map((arg) => {

			// If argument is not an async function - we just return it.
			if (arg.constructor.name !== 'AsyncFunction') return arg;

			// - otherwise we wrap it in a traditional route and return that.
			return (req, res, next, ...args) => {
				// Remark next is not forwarded.
				arg.apply(null, [req, res].concat(args))
					.then(() => {
						if (!res.headersSent) next();
					})
					.catch((err) => {
						next(err);
					});
			};

		});

		// Apply new arguments to old implementation.
		return old.apply(this, args);

	};

});