Is there a way to avoid multiple next() in express middleware

Question

This is how I've designed my route and I'm not really happy with it. I'd rather be able to break down each hasValid into its own middleware, but I don't see how that would work since it wouldn't stop execution.

const secretSender = async (req, res, next) => {
  if (!hasValidA(req)) {
    return next()
  }

  if (!hasValidB(req)) {
    return next()
  }

  if (!hasValidC(req)) {
    return next()
  }

  if (!hasValidD(req)) {
    return next()
  }

  res.send('something secret')
}

router.use(secretSender)
router.get('*', (req, res) => {
  res.send('something public')
})

It also doesn't really make sense to make the default route "something secret" and have "something public" be the middleware since "something public" is the default behavior.

`const checks = [hasValidA, hasValidB, hasValidC, hasValidD]; if (checks.some(c => !c(req))) { return next(); }` — zerkms, Mar 20 '19 at 03:46
why dont you join all your conditions with OR like `if (!hasValidA(req) || !hasValidB(req) ) {return next()}` — Tushar Gupta, Mar 20 '19 at 03:47
_"but I don't see how that would work since it wouldn't stop execution"_... You _can_ stop the `request-response` cycle from a middleware by not calling the `next()` function [[doc](https://expressjs.com/en/guide/using-middleware.html)], see here for example: https://stackoverflow.com/a/33649566/3165255 — IronGeek, Mar 20 '19 at 04:39
@IronGeek if I don't call next then it times out and never sees my "something public" route — Dave, Mar 20 '19 at 04:42
@Dave I'm confused, you wanted the middleware to short-circuit the execution or not? not calling `next()` means you're stopping the execution chain, the request however will still be left hanging. Therefore —and I quote from [the attached answer above](https://stackoverflow.com/a/33649566/3165255)— "so if a middleware needs to end the request-response early, simply do not call `next()` but make sure that the middleware really ends the request-response by calling `res.end`, `res.send`, `res.render` or any method that implicitely calls `res.end`" — IronGeek, Mar 20 '19 at 04:53
@Dave this: _I'd rather be able to break down each hasValid into its own middleware, but I don't see how that would work since it wouldn't stop execution_ — IronGeek, Mar 20 '19 at 05:24

IronGeek · Answer 1 · 2019-03-20T06:34:06.290

Here's one way to break down each hasValid into its own middleware. Each middleware will short-circuit the execution if the outcome is valid:

const validA = async (req, res, next) => {
  if (hasValidA(req)) {
    res.send('something secret') 
  } else {
    next()
  }
}

const validB = async (req, res, next) => {
  if (hasValidB(req)) {
    res.send('something secret')
  } else {
    next()
  }
}

const validC = async (req, res, next) => {
  if (hasValidC(req)) {
    res.send('something secret') 
  } else {
    next()
  }
}

const validD = async (req, res, next) => {
  if (hasValidD(req)) {
    res.send('something secret')
  } else {
    next()
  }
}

router.use(validA, validB, validC, validD)
router.get('*', (req, res) => {
  res.send('something public')
})

Update

To achieve somewhat similiar result with OP's code, but only with single next():

const secretSender = async (req, res, next) => {
  if (hasValidA(req) && hasValidB(req) && hasValidC(req) && hasValidD(req)) {
    res.send('something secret')
  } else {
    next()
  }
}

router.use(secretSender)
router.get('*', (req, res) => {
  res.send('something public')
})

this sends the secret if it meets it single requirement, not what my code does — Dave, Mar 20 '19 at 05:47
To be fair, `hasValid*` here could be anything, a single requirement or even multiple ones depends on how you define it. And each `middleware` here defines it's own _set of requirement(s)_... but i guess this's not what you after... — IronGeek, Mar 20 '19 at 06:30

Is there a way to avoid multiple next() in express middleware

1 Answers1