Maestro for ExpressJS Async Errors

🏆 The async/await heaven!

---

Maestro is a slightly layer of code that acts as a wrapper, without any dependencies, for async middlewares. Its purpose is to ensure that all errors occurring in async operations are properly passed to your stack of error handlers. By doing so, Maestro helps to improve the readability and cleanliness of your code.

Installation:

npm install --save maestro-express-async-errors

or

yarn add maestro-express-async-errors

Note The minimum supported Node version for Maestro is 7.6.0.

How to use it

With maestro:

1const { maestro } = require('maestro-express-async-errors');
2
3
4express.get('/', maestro(async (req, res, next) => {
5	const bar = await foo.findAll();
6	res.send(bar)
7}))

Without maestro:

1express.get('/',(req, res, next) => {
2    foo.findAll()
3    .then ( bar => {
4       res.send(bar)
5     } )
6    .catch(next); // error passed on to the error handling route
7})

So Easy right? 😉

Now let I show you more exemples and functionalities:

• maestro insures thrown errors are passed to next callback:

1const { maestro } = require('maestro-express-async-errors');
2
3app.get('/:id', maestro(async (req, res, next) => {
4    const user = await repository.getById(req.params.id)
5
6    if (!user) {
7      throw new UserNotFoundError
8    }
9
10    res.status(200)
11       .json(user)
12}))
13

• maestro.from allows you to handle a specific error which is helpful for handling domain driven errors.

1
2app.use(maestro.from(UserNotFoundError, (err, req, res, next) => {
3    res.status(404)
4       .json({ error: 'these are not the droids you\'re looking for'})
5})
6
7/**
8  Your error handlers still works as expected. If an error doesn't match your `maestro.from` criteria, it will find its way to the next error handler.
9 */
10app.use((err, req, res, next) => {
11    res.status(500)
12       .json({ error: 'i have a bad feeling about this'})
13})
14

• There's a helper function maestro.all([...]) in case you want to wrap several functions with maestro. With maestro.all, doing [maestro(fn1), maestro(fn2)] can be shortened to maestro.all([fn1, fn2]).

1const maestro = require('maestro-express-async-errors')
2
3// Doing it like this
4app.post('/products', maestro.all([
5    validationFn,
6    createProductFn
7]))
8
9// Is equivalent to this
10app.post('/products', [
11    maestro(validationFn),
12    maestro(createProductFn)
13])

Import in Typescript:

1import { maestro } from "maestro-express-async-errors"

Test Cases

1> maestro-express-async-errors@1.2.5 test
2> mocha --require ts-node/register test/**/*.ts
3
4
5
6  Try maestro(async (req, res, next) => { next() or Error }) :
7    Basic functionality:
8      ✔ Maestro is a function.
9      ✔ Maestro returns a function.
10      ✔ Maestro returns a function that returns a promise.
11      ✔ When an asynchronous function passed into it throws an error, it is expected that the calls next with that error.
12      ✔ When a non-asynchronous function passed into it throws an error, it is expected that calls next with that error.
13      ✔ Should invoke `next` when passing a non-async function.
14      ✔ Thenables are not guaranteed to have a `catch` method. This test refers to this.
15    Should invoke `next` with the thrown error:
16      ✔ If an async function is passed as an argument, the next function should be called with the provided arguments.
17      ✔ Works like a charm if all arguments are passed to the callback function.
18      ✔ Raises a TypeError if next args it's not a function.
19      ✔ A valid call works for routes and middlewares.
20      ✔ A valid call works for error handler middlewares.
21
22  Try maestro.from(RealProblems, (err) => { }) :
23    ✔ Handles the error when error is instance of given constructor.
24    ✔ It call `next` function if error is not an instance of given constructor.
25
26  Try maestro.all([...args]) :
27    ✔ Raises a TypeError when `next` it's not function.
28    ✔ Should return an array.
29    ✔ Should return an array of functions
30    ✔ Should return an array of functions that returns a promise.
31    ✔ Should return an array of functions that returns a promise that calls next.
32    ✔ Should return an array of functions that returns a promise that calls next with the error.
33
34
35  20 passing (75ms)