middleware-async

Async Middleware

A handy tool to write async/promise style middleware for express, connect-like.

Why this tool is needed?

Lets check at this code

app.use(async (req, res, next) => {
  req.user = await User.findById(req.params.id).exec()
  next()
})

The next() will be executed after User.findById(...).exec() is fulfilled because express allow middleware returning Promise.

However, express does not support if promise returned by the middleware is rejected. The followings middlewares will never be called.

Solution is simple by wrapping the middleware with

import middlewaareAsync from 'middleware-async'
app.use(middlewaareAsync(async (req, res, next) => {
  req.user = await User.findById(req.params.id).exec()
  next()  
}))

How to install

Install it via npm or yarn

npm install --save middleware-async
#or
yarn add middleware-async

API

• middlewaareAsync(middlware): return a middleware that covers error thrown or error that is rejected by middleware
• combineMiddlewares(list of middlewares or list of list of middlewares): combine many middlewares into one middleware. Very useful for testing
• middlewareToPromise: convert express-style middleware into Promise
• combineToAsync: combination of middleewareToPromise and combineMiddlewares

Sample usages

import middlewareAsync, {combineMiddlewares, combineToAsync, middlewareToPromise} from 'middleeware-async'

describe('combineMiddlwares', () => {
  it('should go through all middlewares', async () => {
    const req = {val: 0}
    await combineToAsync([
      async (req, res, next) => {
        await Promise.resolve()
        req.val += 1
        next()
      },
      (req, res, next) => {
        req.val++
        next()
      },
    ])(req)
    expect(req.val).to.equal(2)
  })
})