in express how multiple callback works in app.get

Question

I am newbie in node so please forgive me if i am not getting obvious. In node.js express application for app.get function we typically pass route and view as parameters e.g

Answer 1

In Express, each argument after the path is called in sequence. Usually, this is a way of implementing middleware (as you can see in the example you provided).

app.get('/users', middleware1, middleware2, middleware3, processRequest);

function middleware1(req, res, next){
    // perform middleware function e.g. check if user is authenticated

    next();  // move on to the next middleware

    // or

    next(err);  // trigger error handler, usually to serve error page e.g. 403, 501 etc
}