Node Express 4 middleware after routes

Question

Following the upgrade to Express 4, and the removal of app.router, I'm struggling to get middleware to execute after routes execute.

e.g. the following code correctly responds with "hello", but never calls the configured middleware

var express = require( "express" )();

express.get( "/", function( req, res ) {

    res.send( "hello" );

} );
express.use( function( req, res, next ) {

    console.log( "world" );
    next();

} );

express.listen( 8888 );

CLARIFICATION:

the following code shows "before" on the console, but not "after":

var express = require( "express" )();

express.use( function( req, res, next ) {

    console.log( "before" );
    next();

} );
express.get( "/", function( req, res ) {

    res.send( "hello" );

} );
express.use( function( req, res, next ) {

    console.log( "after" );
    next();

} );

express.listen( 8888 );

Answer 1

In regards to Express 4, the "after" function from your second example never gets called because the middle function never calls next().

If you want the "after" function to get called, then you need to add and call the next callback from your middle function like this:

var express = require( "express" )();

express.use( function( req, res, next ) {

  console.log( "before" );
  next();

} );
express.get( "/", function( req, res, next ) {

  res.send( "hello" );
  next();      // <=== call next for following middleware 

} );
express.use( function( req, res, next ) {

  console.log( "after" );
  next();

} );

express.listen( 8888 );

res.send() writes the headers and response back to the client.

Beware, that once res.send() has been called, you won't want to update your response headers or contents. But you can do other tasks like database updates or logging.

Note that express looks at the the number of arguments in the middleware function and does different logic. Take express error handlers for example, which have 4 parameters defined.

express error handler signature: app.use(function(err, req, res, next) {});

Calling next on the very last item in your middleware chain is optional, but probably a good idea in case you ever change things around.

Answer 2

The correct answer is using the res.on("finish", cb) callback.

i.e.:

express.use(function(req, res, next) {
    console.log("before");

    res.on("finish", function() {
        console.log("after");
    });

    next();
});

Answer 3

Have you checked putting your console.log after the next() call?

express.use( function( req, res, next ) {
  next();
  console.log( "world" );
});
express.get( "/", function( req, res ) {
  res.send( "hello" );
});

Answer 4

Order is important http://expressjs.com/4x/api.html#app.use

express.use( function( req, res, next ) {
  console.log( "world" );
  next();
});
express.get( "/", function( req, res ) {
  res.send( "hello" );
});

Answer 5

you can use the Middle ware function in different js file and you can use require function. so that it will be called before and after the http request.

    index.js:     
        const logger = require("./logger");    
           const express = require("express");    
           var app = express();    
           app.listen("3000",()=>console.log("listening on 3000..."))    
        app.use(logger("AppServer"));    
        //get expression    
        app.get("/", function(req,res){    
           console.log("res not received");    
            res.send("Hello World");    
           console.log("res received");    
        })   

    logger.js   

    module.exports = (applicationName) =>{
        return function log(req,res,next){
       console.log(applicationName+" started "+os.hostname);
        res.on("finish",()=>{
            console.log(applicationName+" completed "+os.hostname);
        })
        next();
        }};

output:   
AppServer started hostname-PC   
res not received   
res received   
AppServer completed hostname-PC 

Note: in the logger.js instead of using res.on("finish",callback), you can use req.on("end",callback)