Middleware Email duplicate controls bad code modeling - node.js

Question

I need to add a node.js express middleware for Emails duplicates controls, and a short and easy looking code.
This is my middleware.js file :
// ----------------------------------- MIDDLEWARE FUNCTIONS -------------------------------------------
module.exports = {
/*
* CHECKING FOR DUPLICATE EMAIL
* #params
* #return NEXT()
* #error Status 403s
*/
async duplicate_email(db, req, res, next) {
let availableEmail = await db.collection("users").findOne({ 'email': req.body.email })
if (!availableEmail) {
console.log(" FORBIDDEN ")
res.status(403).send({ errorCode: "403" })
return
} else {
next() // continue the process
}
}
}
And this is my Register web service, in another file called usersCrud.js , I'm struggling since 3 days to make it work but no way :
/*
* Register anonymous user
* #params JSON OBJECT : {}
* #return 200
* #error 400
*/
app.post("/registerUser", middleware.duplicate_email(), function(req, res) {
try {
var user = new User({
_id: null,
prenom: req.body.prenom,
nom: req.body.nom,
email: req.body.email,
password: bcrypt.hashSync(req.body.password, 10),
role: "user",
permissions: middleware.create_permissions("user"),
filenames: [],
groups: [],
last_update: new Date(),
img: "",
birthday: "",
age: "",
job: "",
mentra: "",
});
db.collection("users").insertOne(user);
console.log("Added one user");
res.sendStatus(200);
} catch (e) {
console.log(e);
res.sendStatus(400);
}
});
This is the error :
Error: Route.post() requires a callback function but got a [object Promise]
I have tried tons of things, like adding the db parameter, use a return function, removing all parameters, but I can' t make it work. The code would be really simplier if that thing could work like this, but I don't know if it is possible.
Maybe it is easy to solve for you .

Answer 1

The error message tells you what's wrong, since you invoke middleware.duplicate_email() in your app.post and thus returns a promise. You need to pass the function without invoking it or define it as a factory function that returns the middleware and takes the db object as a parameter. I'd go with the second approach, which would look something like:
module.exports = {
duplicate_email(db) {
return async (req, res, next) => {
let availableEmail = await db.collection("users").findOne({'email': req.body.email})
if (!availableEmail) {
console.log(" FORBIDDEN ")
res.status(403).send({errorCode: "403"})
return
} else {
next() // continue the process
}
}
}
}
You can then use it like this:
app.post("/registerUser", middleware.duplicate_email(db), function(req, res) { ... }

Answer 2

Have you tried to do something like this?
app.post("/registerUser", await middleware.duplicate_email(), function(req, res)
It has to be included in the async function of course to be able to use the await keyword. As the error says, the callback is expected, but you provided a not resolved Promise.
Another thing that may work is:
app.post("/registerUser", async () => {
const result = await middleware.duplicate_email();
return result;
}, function(req, res) {
// stuff
}