How to combine two middleware and export as one?

Question

I have a utility file which basically has two functions (one to detect user location and another to get user device details) acting as middlewares. Now I would like to know whether it is possible to combine both the middlewares together as one so that it could be used with other middlewares on the route. I would also like to have the freedom of using the functions in the utility file individually when required.

Utility file

const axios             = require("axios");
const requestIp         = require("request-ip");

const getDeviceLocation = async (req, res, next) => {
    try {
        // ToDO: Check if it works on production
        const clientIp  = requestIp.getClientIp(req);
        const ipToCheck = clientIp === "::1" || "127.0.0.1" ? "" : clientIp;

        const details = await axios.get("https://geoip-db.com/json/" + ipToCheck);

        // Attach returned results to the request body
        req.body.country    = details.data.country_name;
        req.body.state      = details.data.state;
        req.body.city       = details.data.city;

        // Run next middleware
        next();
    }
    catch(error) {
        return res.status(500).json({ message: "ERROR_OCCURRED" });
    }
};

const getDeviceClient = async (req, res, next) => {
    const userAgent = req.headers["user-agent"];

    console.log("Device UA: " + userAgent);
    next();
};

module.exports = { getDeviceLocation, getDeviceClient };

Example Routes

app.post("/v1/register", [getDeviceLocation, getDeviceClient, Otp.verify], User.create);

app.post("/v1/auth/google", [getDeviceLocation, getDeviceClient, Auth.verifyGoogleIdToken], Auth.useGoogle);

I would like to have getDeviceLocation and getDeviceClient combined into one say getDeviceInfo yet have the freedom to use getDeviceLocation and getDeviceClient individually when required on any route.

score 5 · Answer 1 · answered Jan 05 '21 at 22:38

Express allows you to declare middleware in an array, so you can simply define an array of the middlewares you'd like to combine:

const getDeviceLocation = async (req, res, next) => {
...
};

const getDeviceClient = async (req, res, next) => {
...
};

const getDeviceInfo = [getDeviceLocation, getDeviceClient];

module.exports = { getDeviceLocation, getDeviceClient, getDeviceInfo };

You can then use any combination of one or both of the middleware wherever you like:

app.use('/foo', getDeviceLocation, () => {});
app.use('/bar', getDeviceClient, () => {});
app.use('/baz', getDeviceInfo, () => {});

Rami Jarrar · Accepted Answer · 2019-06-01T17:47:30.510

1

In your case maybe you can use something simple like this

const getDeviceInfo = async (req, res, next) => {
    await getDeviceClient(req, res, async () => {
        await getDeviceLocation(req, res, next)
    })
}

But you may need to handle error cases.

edited Jun 01 '19 at 17:47

answered Jun 01 '19 at 17:21

Rami Jarrar

4,523
7
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In that case I won't be able to use the individual functions independently, I guess. – Ayan Jun 01 '19 at 17:22
no you can still use them! you just create this as another function/middleware. – Rami Jarrar Jun 01 '19 at 17:23
Can it be used with await ? – Ayan Jun 01 '19 at 17:28
what do you mean?! – Rami Jarrar Jun 01 '19 at 17:29
I meant can it be done like `await getDeviceClient(req, res, next); await getDeviceLocation(req, res, next);` – Ayan Jun 01 '19 at 17:31
not if you want to use the individual functions independently – Rami Jarrar Jun 01 '19 at 17:33
Actually my IDE says `Promise returned is ignored`, so I thought of asking. – Ayan Jun 01 '19 at 17:34
ah that's why I told you `But you may need to handle error cases.`, but anyway to remove that error just add await before each call, I'll update the answer – Rami Jarrar Jun 01 '19 at 17:36
I guess you are missing a async statement on the first await function. – Ayan Jun 01 '19 at 17:46
:) Looks like that's what I wanted. Thank you. – Ayan Jun 01 '19 at 17:50

score 1 · Answer 3 · answered Dec 07 '20 at 16:00

If you'd like to avoid callback hells you can use something like this:

const nextInterceptor = error => {
  if (error) { throw error; }
};

const combineMiddlewares = middlewares => (req, res, next) => (
  middlewares.reduce((previousMiddleware, currentMiddleware) => (
    previousMiddleware.then(() => currentMiddleware(req, res, nextInterceptor))
  ), Promise.resolve())
    .then(() => next())
    .catch(next)
);

const commonMiddlewares = combineMiddlewares([getDeviceLocation, getDeviceClient]);

app.post("/v1/register", [commonMiddlewares, Otp.verify], User.create);
app.post("/v1/auth/google", [commonMiddlewares, Auth.verifyGoogleIdToken], Auth.useGoogle);

score 0 · Answer 4 · answered Jun 01 '19 at 16:23

0

Using connect nodemodule you can do combine the middle ware and expose a new end point for it. Ref here a sample code https://blog.budiharso.info/2015/07/28/Combine-multiple-express-middleware/

answered Jun 01 '19 at 16:23

Senthil

2,156
1
14
19

1

Yes, I have gone through it before asking here but it asks for connect package. Is there any other alternative way of doing? – Ayan Jun 01 '19 at 16:25
In the code which you posted you are following the chaining multiple middle ware calls without using any third party module Ref: https://stackoverflow.com/questions/31928417/chaining-multiple-pieces-of-middleware-for-specific-route-in-expressjs – Senthil Jun 01 '19 at 16:34
If you still want to expose a different route, then using node modules 3rd party like combine, compose-middleware, middleware-flow are the other options. – Senthil Jun 01 '19 at 16:35
Which one do you suppose is better. I haven't used any of them. – Ayan Jun 01 '19 at 16:37
combine is better – Senthil Jun 01 '19 at 16:49

plashenkov · Answer 5 · 2021-07-04T23:54:19.267

It's simple and doesn't require to install anything. Just use:

const {Router} = require('express')

const combinedMiddleware = Router().use([middleware1, middleware2, middleware3])

Now you can use combined middleware where necessary. For example:

app.get('/some-route', (req, res, next) => {
  req.query.someParam === 'someValue'
    ? combinedMiddleware1(req, res, next)
    : combinedMiddleware2(req, res, next)
})

How to combine two middleware and export as one?

5 Answers5