the correct way using middleware in express

Question

hey I want to make sure if I use the correct way for middleware in my simple express app, I am trying to find the email unique for register here is my example

const isUnique = (req, res, next) => { User.findOne({ where:{ email: req.body.email } }) .then(getUser => { if(getUser){ next("/userAlreadyExist") // router // or can i render to to html? i am using ejs } else { next() } }) .catch(next()) } app.post('/register', isUnique ,(req, res) => { res.send(`thank you for register`) }

I want to make sure the email already exists or no, so I want to pass it on middleware first, and get a page for isUnique, if the email already in use, I want to redirect it to next router called '/emailExist', and if it success i want to redirect it to router /success can anyone help me if that code wrong or no? just want to make sure :D

miyu · Accepted Answer · 2019-03-23 01:44:26Z

You have a lot of options, here are a couple.

You can redirect users to specific pages based on whether or not the email exists. Within your /emailAlreadyExists and /registerSuccess routes you can render whatever templates you want or return some data.

const isUnique = (req, res, next) => { User.findOne({ where:{ email: req.body.email } }) .then(getUser => { if (getUser) { res.redirect('/emailAlreadyExists'); } else { res.redirect('/registerSuccess'); // or just call next() } }) .catch(next("DB error")); }

Pass along the results of the db query and let your final middleware handle it:

const isUnique = (req, res, next) => { User.findOne({ where:{ email: req.body.email } }) .then(getUser => { req.user = getUser; next(); }) .catch(next()); } app.post('/register', isUnique ,(req, res) => { if (req.user) { res.send('User already exists'); } else { res.send(`thank you for register`); } }

You can also create an error handling middleware:

const isUnique = (req, res, next) => { User.findOne({ where:{ email: req.body.email } }) .then(getUser => { if(getUser){ next("Error: user already exists"); // or some other error message/object } else { next(); // continue to next middleware } }) .catch(next("DB error")); // handle errors throw from DB read } app.post('/register', isUnique ,(req, res) => { res.send(`thank you for register`) } /* If you call "next" with an argument, Express will skip straight to this error handler route with the argument passed as the "err" parameter */ app.use((err, req, res, next) => { console.error(err.stack); res.status(500).send(`An error occurred: ${err}`); })

how about if i want to handle the next router if the user already exist ??:D
if user not exist we redirect it to next router, it meant we not usse middle ware ? because we stop it ? so is that best way to call next() for the else ?
Express middleware are a sequence of functions that process a single request. When you call next(), you are handing control over to the next middleware function in the sequence. So in app.post('/register', isUnique, (req, res) => ...), if you call next() with no arguments inside isUnique, you will pass control into the (req, res) => ... function. You can check out the Express middleware docs, and if you're still lost try putting print statements in your functions and see what happens

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