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.

Answer 1

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, () => {});

Answer 2

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.

Answer 3

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);