问题
I am newbie in node so please forgive me if i am not getting obvious. In node.js express application for app.get function we typically pass route and view as parameters e.g.
app.get('/users', user.list);
but in passport-google example I found that they are calling it as
app.get('/users', ensureAuthenticated, user.list);
where ensureAuthenticated is a function
function ensureAuthenticated(req, res, next) {
if (req.isAuthenticated()) { return next(); }
res.redirect('/login')
}
In short this means there are multiple callbacks which while running are called in series. i tried adding couple of more functions to make it look like
app.get('/users', ensureAuthenticated, dummy1, dummy2, user.list);
and i found ensureAuthenticated, dummy1, dummy2, user.list is getting called in series.
for my specific requirement i find calling functions sequentially in above form is quite elegant solution rather that using async series. can somebody explain me how it really works and how i can implement similar functionality in general.
回答1:
In Express, each argument after the path is called in sequence. Usually, this is a way of implementing middleware (as you can see in the example you provided).
app.get('/users', middleware1, middleware2, middleware3, processRequest);
function middleware1(req, res, next){
// perform middleware function e.g. check if user is authenticated
next(); // move on to the next middleware
// or
next(err); // trigger error handler, usually to serve error page e.g. 403, 501 etc
}
来源：https://stackoverflow.com/questions/22285677/in-express-how-multiple-callback-works-in-app-get