function for app.get callback in express.js

Question

function for app.get callback in express.js

Hey there, I'm a bit puzzled by the syntax of the get route function because there seem to be two versions. Here's an example of some 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'm confused about the purpose of the 'next' function in the second one and why it isn't necessary in the first one.

Thanks!

javascript express get

Answer 1

Answer №1

Consider taking a step back and viewing express as a middleware stack, much like a literal stack.

With a series of app.use, app.get, and app.post calls, you create a chain of middleware functions. When a request is received, express identifies which middleware functions match the URL pattern and calls the first one, passing along a reference to the next in line. This is how separate, independent middleware objects become interconnected.

For instance, there are middleware functions that parse query strings into an object stored in req.query, handle cookie header parsing, and provide access logging. These functions are linked together in a cohesive chain, with each passing control to the next by invoking 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 typically don't use next is because they often mark the end of a middleware chain. After reaching a route, there's usually no further processing needed.

Answer 2

Consider taking a step back and viewing express as a middleware stack, much like a literal stack.

With a series of app.use, app.get, and app.post calls, you create a chain of middleware functions. When a request is received, express identifies which middleware functions match the URL pattern and calls the first one, passing along a reference to the next in line. This is how separate, independent middleware objects become interconnected.

For instance, there are middleware functions that parse query strings into an object stored in req.query, handle cookie header parsing, and provide access logging. These functions are linked together in a cohesive chain, with each passing control to the next by invoking 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 typically don't use next is because they often mark the end of a middleware chain. After reaching a route, there's usually no further processing needed.

function for app.get callback in express.js

Answer №1

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