express-async-error-handling.js

require("dotenv").config();
const express = require("express");
const morgan = require("morgan");
const cors = require("cors");
const helmet = require("helmet");
const { NODE_ENV } = require("./config");

const app = express();

const morganOption = NODE_ENV === "production" ? " tiny" : "common";


const pc = async (fn) => {
  try {
    const retVal = await fn()
    return [null, retVal]
  } catch (error) {
    return [error, null]
  }
}

const asyncHelper = (value, error = null) => {
  return new Promise((resolve, reject) => {
    setTimeout(() => {
      if (error) {
        reject(error)
      } else {
        resolve(value)
      }
    }, Math.random() * 1000 * 3)
  })
}

const dataService = {
  getRand: async () => {
    return asyncHelper(null, new Error('NO_ENTROPY'))
    // return asyncHelper(42)
  }
}

app.use(morgan(morganOption));
app.use(helmet());
app.use(cors());

app.get("/", (req, res) => {
  x.nothing() //this breaks
  res.send("<h1>Hello, world!</h1>");

});


app.get("/api/rand", async (req, res, next) => {
  // const [error, value] = await pc(()=>43)
  const [error, value] = await pc(dataService.getRand)
  if (error) {
    // return next(error)
    return req.redirect('/login')
  }
  res.json({ value })

  /*
  //standard try-catch without pc the helper
  try {
    const value = await dataService.getRand()
    res.json({ value })

  } catch (err) {
    return next(err)
  } */
});

app.use(function erroHandler(error, req, res, next) {
  const isAPI = /^\/api\//g.test(req.path)
  if (!isAPI) {
    return res.status(500).send(`
    <pre>
      ${error}
      ${error.stack}
    </pre>
    `)
  }

  let response;
  if (NODE_ENV === "production") {
    response = { error: { message: "server error" } };
  } else {
    console.error(error);
    response = { message: error.message, error };
  }
  res.status(500).json(response);
});

module.exports = app;