How can i stop further execution of express middleware - mysql

Question

I want to get this functionality if(thereIsSomeError) //stop executing further. for example if there some error accurs in middleware or in the callback then i don't want to execute callback(in the app.route) and the middleware further
I tried this code. But i'm still getting req.err as true. how can i fix this issue
// My MiddleWare
export let Middleware=()=> {
return (req,res,next)=>{
next()
console.log(req.err) // Problem is here.. i'm still getting req.err(true)
if(!req.err){
db.query(`query`,(error, responseData)=>{
if(error) console.log(error)
db.query(`second query`,{...// send data to the
database})
})
}
}
}
//End point
app.post('/addStudent',Middleware, (req, res) => {
//setting error to true initially
req.err=true;
let data = req.body
db.query(`query `, data.username, (err, d) => {
if (err) return res.json(err)
else {
// since no Error accured so set the error to false
req.err=false;
let q = 'query';
let values = {//data here}
db.query(q, values, (err, data) => {
if (err) return res.status(200).json(err)
else return res.status(200).json({ data })
})
}
})
})

Answer 1

First, a middleware runs BEFORE a request, NOT AFTER. If you set req.err = true in your POST endpoint, IT WILL STAY TRUE, meaning your database call will certainly return an error.
Second, to successfully abort a middleware call, use return. Returning a function stops it immediately. You can choose either to return next(err) to forward the error to the handler, or to use return res.send('Error') to terminate the response in the middleware.