What is the parameter next used for in Express?

Express is a minimal and flexible Node.js web application framework that provides a robust set of features to develop web and mobile applications . It facilitates the rapid development of Node based Web applications.

Middleware functions are functions that have access to the request object ( req ), the response object ( res ), and the next middleware function in the application’s request-response cycle. The next middleware function is commonly denoted by a variable named next .

So, calling next() from inside a route simply tells Express that it should proceed with the remainder of the route and then move on to the next matching route . Contrast this with calling return next() from within a route.

Next simply allows the next route handler in line to handle the request . In this case, if the user id exists, it will likely use res. send to complete the request. If it doesn’t exist, there is likely another handler that will issue an error and complete the request then.