表达js app.get回调函数

Question

hi I am confused about the syntax of the get route function there seems to be 2 versions here is some example code

first one:

app.get('/users', function(req,res){
     ...
});

second one:

app.get('users/:name', function(req,res,next){
     ...
     if(users[req.params.name])
      ....
     else
         next()
});

I am confused as to what is the next function in the second one. And why it isn't necessary in the first one

Thanks

Answer 1

Back it up a bit and look at express as a middleware stack. Literally, a stack.

You have a series of app.use , app.get , and app.post calls. Together, they form a chain. When a request comes in, express figures out which middleware functions match the URL pattern and calls the first one along with a reference to the next one. This is how separate, independent middleware objects get linked.

For example, there is a middleware that parses the query string and stores it as an object in req.query . There is a middleware that parses the Cookie header and creates cookie objects. There is a middleware that provides access logging. Again, these get linked together as a chain. If the middleware functions are independent, they do their work and then pass control to the next link in the chain by calling next() .

app.use(express.logger();
app.use(express.responseTime());
app.use(express.compress());
app.use(express.json());
app.use(express.urlencoded());
app.use(express.cookieParser());
app.use(express.session());
app.use(i18n.handle);
app.use(app.router);

The reason routes do not have to use next is because routes are generally the end of a chain. There is nothing left to do after a route.