Order of router precedence in express.js

Question

I would like to understand the order precedence in express.js. For example, as bellow code

var routes = require('./routes/index');
var users = require('./routes/users');
var api = require('./routes/api');


app.use('/api', api);
app.use('/users', users);

app.use('/:name', function(req, res, next) {    
    console.log('from app.js name:', req.params.name);   

    res.render('index', {
        title: req.params.name
    });
}, routes);

app.use('/', function(req, res, next) {   
    res.render('index', {
        title: 'MainPage'
    });
});

If a request come from client localhost:3000/api/abc and localhost:3000/user/abc, the response from api and user module. But if I make a request like localhost:3000/myName/xyz, the app module return a response. This behavior let me concern about what is precedence of expressjs and what is correct order for router modules. Why routers do not confuse between actions "api", "users" and parameter ":name". Please let me understand clearly how express does and what is precedence.

Laxmikant Dange · Accepted Answer · 2018-06-14T04:17:34.497

The order is first come first serve.

In your case, if user hits /api, he will get response from api, but if you write /:name route before /api, /:name will serve for /api requests also.

Case1: /api will serve requests for /api.

var routes = require('./routes/index');
var users = require('./routes/users');
var api = require('./routes/api');


app.use('/api', api);
app.use('/users', users);

app.use('/:name', function(req, res, next) {    
    console.log('from app.js name:', req.params.name);   

    res.render('index', {
        title: req.params.name
    });
}, routes);

app.use('/', function(req, res, next) {   
    res.render('index', {
        title: 'MainPage'
    });
});

Case2: /:name serves requests for /api and /users

var routes = require('./routes/index');
var users = require('./routes/users');
var api = require('./routes/api');

app.use('/:name', function(req, res, next) {    
    console.log('from app.js name:', req.params.name);   

    res.render('index', {
        title: req.params.name
    });
}, routes);

app.use('/api', api);
app.use('/users', users);



app.use('/', function(req, res, next) {   
    res.render('index', {
        title: 'MainPage'
    });
});

Thank too much @Laxmikant Dange but if I do nothing in api module or users modules, why the app.use("/", func(){}) acts as server...?. It responses the MainPage..?? — hoanganh17b, Sep 16 '15 at 09:13
Where in the ExpressJS documentation, can I find information about precedence rules of use() and get() routes. — Michael R, Sep 12 '16 at 19:53
@hoan because there is no `:name` so it doesn't match `/:name` — Gabriel Bleu, Oct 27 '17 at 08:38

score 4 · Answer 2 · answered Mar 25 '21 at 16:00

The example given in the ExpressJS documentation is pretty simple and was unfortunately difficult to find. I only found it through another SO question.

Middleware functions are executed sequentially, therefore the order of middleware inclusion is important

app.use(function(req, res, next) {
    res.send('This is the only thing that ever happens')
}
app.use(...) // never used
app.get(...) // never used
app.put(...) // never used
app.post(...) // never used

Order of router precedence in express.js

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