Async error handling

async-error.ts

import debug from 'debug';
import express, { NextFunction, Request, Response } from 'express';

const testRouter = express.Router();

const delay = async (wait: number, label: string) =>
  new Promise(resolve => {
    debug('yncx:delay:start')({ wait, label });
    setTimeout(() => {
      debug('yncx:delay:end')({ wait, label });
      resolve(wait);
    }, wait);
  });

const withCatch = (
  f: (...args: any[]) => Promise<any>,
): ((...args: any[]) => Promise<any>) => (...args) =>
  f(...args).catch(error => {
    throw error;
  });

async function doSomeAsyncTask(wait: number) {
  debug('yncx:doSomeAsyncTask')({ wait });
  await delay(wait, 'doSomeAsyncTask');
  debug('yncx:doSomeAsyncTask')('Throwing error');
  throw new Error('Test async error');
}

async function test() {
  debug('yncx:test')({});
  const promiseIcanWaitFor = withCatch(doSomeAsyncTask)(100);

  const somethingElse = delay(200, 'test:somethingElse');

  const result = await Promise.all([promiseIcanWaitFor, somethingElse]);
  debug('yncx:test:result')({ result });
}

const testMiddleware = async (
  req: Request,
  res: Response,
  next: NextFunction,
) => {
  try {
    await test();
    debug('yncx:testMiddleware')('OK');
    next();
  } catch (error) {
    debug('yncx:testMiddleware')('Caught error');
    // You'd normally pass this onto the next() error handler here:
    res.status(500).send({
      error: error.message,
    });
  }
};

testRouter.use(testMiddleware);
testRouter.get('/async-error-test', async (req: Request, res: Response) => {
  return res.sendStatus(200);
});

export default testRouter;

curl

curl -i http://localhost:8080/async-error-test

HTTP/1.1 500 Internal Server Error
X-Powered-By: Express
Content-Type: application/json; charset=utf-8
Content-Length: 28
ETag: W/"1c-3N4A5kSM7ex++ACAGIND7W0R29c"
Date: Tue, 09 Jul 2019 20:43:02 GMT
Connection: keep-alive

{"error":"Test async error"}

debug.log

  yncx:test {} +0ms
  yncx:doSomeAsyncTask { wait: 100 } +0ms
  yncx:delay:start { wait: 100, label: 'doSomeAsyncTask' } +0ms
  yncx:delay:start { wait: 200, label: 'test:somethingElse' } +0ms
  yncx:delay:end { wait: 100, label: 'doSomeAsyncTask' } +0ms
  yncx:doSomeAsyncTask Throwing error +0ms
  yncx:testMiddleware Caught error +0ms
  yncx:delay:end { wait: 200, label: 'test:somethingElse' } +0ms