node.js/JavaScript syntax - add extra parameter to passed parameters

Question

I'm building a REST API using node.js/Express.

I have some middleware applied to certain routes. I have a JavaScript syntax error which I can't resolve.

server.js

const express = require('express')
const router = express.Router()


const watchdogController = {
  ping: function(req, res, next) {
    console.log('watchdog')
    res.status(200).send('woof!')
    //next()
  }
}
const middleware = function(req, res, next) {
  console.log('middleware')
  next()
}
const middleware2 = function(req, res, next, roles) {
  console.log('middleware2')
  //console.log(roles)   //I want to be able to view the roles here!
  next()
}


//This line is where I have the issue...
router.get('/watchdog', middleware, middleware2, watchdogController.ping)



module.exports = router

I need to be able to pass an array of roles to middleware2. E.g.

router.get('/watchdog', middleware, middleware2(...['ordinary','supervisor']), watchdogController.ping)

But this syntax fails :(

node server.js results in:

middleware2
undefined
/Users/asdf7/Desktop/asdf7/lib/router.js:19
  next()
  ^

TypeError: next is not a function
    at middleware2 (/Users/asdf7/Desktop/eoh/lib/router.js:19:3)
    at Object.<anonymous> (/Users/asdf7/Desktop/eoh/lib/router.js:26:37)
    at Module._compile (internal/modules/cjs/loader.js:701:30)
    at Object.Module._extensions..js (internal/modules/cjs/loader.js:712:10)
    at Module.load (internal/modules/cjs/loader.js:600:32)
    at tryModuleLoad (internal/modules/cjs/loader.js:539:12)
    at Function.Module._load (internal/modules/cjs/loader.js:531:3)
    at Module.require (internal/modules/cjs/loader.js:637:17)
    at require (internal/modules/cjs/helpers.js:22:18)
    at Object.<anonymous> (/Users/asdf7/Desktop/asdf7/index.js:2:16)

This works:

router.get('/watchdog', middleware, middleware2, watchdogController.ping)

But now I can't see any roles in middleware2 ;( I need to be able to view the roles array in the middleware2 function.

I can't figure out what syntax to use... Can you guys help?

As long as whatever is in the params to get is a middleware, you can create that middleware however you want. The easiest would be to create a function that returns your middleware--and you'd pass your roles into the middleware creator function. — Dave Newton
– Dave Newton, Commented May 14, 2019 at 12:53
A middleware in express has next format (req, res, next). If you need to pass info, you must attach this info to the request in a previous middlewares, example on middleware1 you can add req.roles = 'WHATEVER'; and after the next call, you would be able to access to req.roles on middleware2. — Jose Mato
– Jose Mato, Commented May 14, 2019 at 12:56
@DaveNewton Really appreciate your reply. I'm not sure how this would work. Create middleware? The best I can come up with sofar is replace middleware2 with: (req,res,next) => { middleware2(req,res,next,['ordinary','supervisor']) }. I thought I could use the spread operator, but not sure how to... — Mr Ed
– Mr Ed, Commented May 14, 2019 at 12:56
@JoseMato I have several dozen routes (not just '/watchdog'). I'm trying to pass the roles alongside the route to keep the syntax clean. middleware1 is an isolated function for auth. I don't want it to stuff parameters (and figure out what parameters to stuff). I just want to inject the roles array on the same line as where the route is defined. My goal here is clean syntax rather than "making it work". — Mr Ed
– Mr Ed, Commented May 14, 2019 at 12:59
No. createMiddleware2 = roles => { return function (req, res, next) { doSomethingWithRolesEtc... } } — Dave Newton
– Dave Newton, Commented May 14, 2019 at 13:04

Mr Ed · Accepted Answer · 2019-05-14 13:45:37Z

1

Solution (with thanks to @DaveNewton):

const express = require('express')
const router = express.Router()


const watchdogController = {
  ping: function(req, res, next) {
    console.log('watchdog')
    res.status(200).send('woof!')
    //next()
  }
}
const middleware = function(req, res, next) {
  console.log('middleware')
  next()
}
const middleware2 = roles => function(req, res, next) {
  console.log('middleware2')
  console.log(roles)
  next()
}

router.get('/watchdog', middleware, middleware2(['ordinary','supervisor']), watchdogController.ping)



module.exports = router

answered May 14, 2019 at 13:45

Mr Ed

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1 Comment

Dave Newton Over a year ago

Glad it worked out. Note that there may be other and/or better solutions to this, especially as I haven't used Express for a long time now--poke around in their middleware docs and look at some examples to see if there's a cleaner way.

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