What are the situations in which you can't do without app.param in Express?

Question

Node.js

In what situations can you not do without app.param? After all, actions can be done immediately in app.get.

app.param('userId', (req, res, next) => {
    // some actions
    next()
})

app.get('/users/:userId', (req, res) => {
    // some actions
    res.end()
})

Answer 1

There are no such situations, but sometimes it is more convenient with him.
For example, when you have several different routes with this parameter.

app.param('userId', (req, res, next) => {
  // тут какой-то длинный код
  next();
});

app.get('/users/:userId', (req, res) => { ... });
app.get('/users/:userId/info', (req, res) => { ... });
app.post('/users/:userId', (req, res) => { ... });

There was no need to write the same code in all routes.