Express all issue - express

Question

I docs it said that this two way of defining two sequential midlewares are equivalent
http://expressjs.com/4x/api.html#app.all
app.all('*', requireAuthentication, loadUser);
Or the equivalent:
app.all('*', requireAuthentication)
app.all('*', loadUser);
But it if we have middlewares defined as:
var requireAuthentication = function(req, res, next){
req.params.someParam = 1
next()
}
var loadUser = function(req, res, next){
console.log('someParam', req.params.someParam)
...
}
In first case req.params.someParam inside loadUser will be 1, and in second case it will be undefined.
Is it a bug or wat?

Answer 1

In short: req.params doesn't persist across routes. Use res.locals instead.
Not a bug in Express, but not very intuitive. This is a good question!
req.params is for grabbing parameters out of a URL. For example, if you had a route defined like this...
app.get('/user/:id', function(req, res) {
res.send('user id == ' + req.params.id);
});
...and you visited /user/123, then req.params.id would be "123".
This params property is different for every route. Take a look at this example:
app.get('/user/:userid', function(req, res, next) {
// req.params.userid is defined in here
// req.params.id is NOT defined here
next();
});
app.get('/user/:id', function(req, res) {
// req.params.id is defined in here
// req.params.userid is NOT defined here
});
req.params isn't the same for every route, which explains what you're seeing.
Your first example has one route with two request handler functions, so they all have access to the same req.params object. Your second example has two routes with two request handler functions, so they're accessing different req.params objects.
If you're trying to persist data between different request handler functions across the same request, you should use res.locals. To rewrite your example:
var requireAuthentication = function(req, res, next){
res.locals.someParam = 1
next()
}
var loadUser = function(req, res, next){
console.log('someParam', res.locals.someParam)
...
}
Using res.locals will work whether you have one line or two.
Hope that helps!