express-rescue

Express Rescue

It's a wrapper for async functions which makes sure all async errors are passed to your error handler preventing those anoing UnhandledPromiseRejectionWarning when using async/await, especially with expressjs routes/middlewares. And nope, this is not an anti-pattern.

Usin with expressjs

It's so simple... how about I just show you how it's done?

const rescue = require('express-rescue')

// ...

app.get('/:id', rescue(async (req, res, next) => {
    const user = await repository.getById(req.params.id)

    if (!user) {
      throw new UserNotFoundError
    }

    res.status(200)
       .json(user)
}))

app.use((err, req, res, next) => {
  if (err instanceof UserNotFoundError) {
    return res.status(404)
              .json({ error: 'these are not the droids you\'re looking for'})
  }

  res.status(500)
     .json({ error: 'i have a bad feeling about this'})
})

That's all. Told you it was simple, right?

Using anywhere else

It was intended to be use with expressjs but I'm pretty sure you could use it anywhere you want since you pass your error handler as the last argument.

Let's try it out:

const rescue = require('express-rescue')

const somethingWrong = rescue(function (arg1, arg2, arg3, arg4, errorHandler) {
  throw new Error('Houston, we have a problem!')
})

const arg1 = null
const arg2 = null
const arg3 = null
const arg4 = null

const errorHandler = function (err) {
  console.log(err.message)
  process.exit(1)
}

somethingWrong(arg1, arg2, arg3, arg4, errorHandler) // Houston, we have a problem!

Oh in case you didn't notice: yes, you're not limited to use only async functions. somethingWrong is a regular (sync) function.

Hope you enjoy the async/await heaven!

Chears!

Tests

yarn test v0.27.5
$ mocha specs --require ./specs/spec-helper.js


  const callable = rescue(async ([err,] req, res, next) => { })
    calls the last argument (next) with the thrown error
      ✓ Raises a TypeError if last argument is not a function
      ✓ callable(req, res, next) - works for routes and middlewares
      ✓ callable(err, req, res, next) - works for error handler middlewares
      ✓ callable(foo, bar, baz, foobar, foobaz, errorHandler) - should work for basically anything, since you place an error handler as the last argument


  4 passing (17ms)

Done in 0.48s.