Express middleware getting called many times

Question

app.use(function(req, res, next) {
    var chatlog = [];
    console.log('executed many timews why?')   
 var chatlog = redisClient.lrange('messages', 0, 99, function(err, reply) {
        if (!err) {
            var result = [];
            for (var msg in reply) result.push(JSON.parse(reply[msg]));
            if (result.length == 0) { 
                result.push({
                    "msg": 'welcome',
                    "nickname": "guest1"
                })
            }
            console.log(result)
        } else {
            console.log('error getting chat messages')
        }
        res.locals = {
            chatlog: result
        };
        next();
        return
    });

  app.get('/', (req, res) => {
 res.render('index', {     })
  })

When I visit '/' once, console prints the following:

executed many timews why
[ { msg: 'welcome', nickname: 'guest1' } ]
executed many timews why
executed many timews why
executed many timews why
executed many timews why
[ { msg: 'welcome', nickname: 'guest1' } ]
[ { msg: 'welcome', nickname: 'guest1' } ]
[ { msg: 'welcome', nickname: 'guest1' } ]
[ { msg: 'welcome', nickname: 'guest1' } ]
executed many timews why
executed many timews why
[ { msg: 'welcome', nickname: 'guest1' } ]
[ { msg: 'welcome', nickname: 'guest1' } ]
executed many timews why
[ { msg: 'welcome', nickname: 'guest1' } ]

How can I make my middleware to execute only once? If I take away next, it runs only once but page won't load, and if I keep next(), it executes many times.

Answer 1

Your middleware is set up to get called for each request. This means that with an incorrectly configured Express, it will get called for each image-, stylesheet- or JS-file that you happen to be using in your index template.

If those files are served by express.static, make sure that your middleware gets loaded after the express.static declaration:

app.use(express.static(...));

app.use(...your middleware...);

app.get('/', ...);

This way, your middleware won't be called for the static resources because express.static will handle them before your middleware.

You can also create a separate middleware function and insert it into specific routes:

let myMiddleware = function(req, res, next) {
  ...
});

app.get('/', myMiddleware, function(req, res) {
  res.render('index', {})
});