Express Routing

Routing determines how an application responds to a client request for a specific endpoint, a combination of a URL path and an HTTP method. This lesson covers how Express matches and dispatches requests to the right handler.

What Is Routing in Express?

A route in Express is defined by calling a method named after an HTTP verb, app.get(), app.post(), app.put(), app.delete(), and passing it a path and one or more handler functions.

When a request arrives, Express walks through registered routes in the order they were defined and dispatches to the first one whose method and path both match.

app.get('/', (req, res) => {
  res.send('Home page');
});

app.get('/about', (req, res) => {
  res.send('About page');
});

app.post('/users', (req, res) => {
  res.status(201).json({ created: true });
});

Each route pairs an HTTP method with a path. GET / and GET /about are different routes even though they share the same method.

Route Definition Syntax

app.METHOD(PATH, HANDLER)

// examples
app.get('/users', handler);
app.post('/users', handler);
app.put('/users/:id', handler);
app.delete('/users/:id', handler);
app.all('/health', handler); // matches any method

METHOD is any HTTP verb in lowercase: get, post, put, patch, delete.
PATH can be a plain string, a string with named parameters (:id), or a regular expression.
HANDLER receives (req, res, next) and is responsible for sending a response.
app.all() matches a path regardless of HTTP method.

Express Routing Cheatsheet

The most common routing patterns you will write in nearly every Express app.

Pattern	Example	Matches
Exact path	`app.get('/about', fn)`	`GET /about` only
Named parameter	`app.get('/users/:id', fn)`	`GET /users/42`, `req.params.id === '42'`
Multiple params	`app.get('/users/:userId/posts/:postId', fn)`	Nested resource paths
Optional segment	`app.get('/products/:id?', fn)`	`/products` and `/products/5`
Any method	`app.all('/status', fn)`	GET, POST, PUT, DELETE, etc.
Chained methods	`app.route('/users').get(a).post(b)`	Same path, multiple methods

Route Matching Order Matters

Express checks routes top to bottom and stops at the first match unless that handler calls next(). This means a generic route defined earlier can accidentally "shadow" a more specific one defined later.

// BAD: this catches everything, /new never gets a chance to run
app.get('/users/:id', getUserById);
app.get('/users/new', showNewUserForm);

// GOOD: specific literal paths before parameterized ones
app.get('/users/new', showNewUserForm);
app.get('/users/:id', getUserById);

Always place more specific, literal paths before parameterized wildcard-style paths.

Organizing Routes as Your App Grows

Defining every route directly on app works for small examples, but real applications quickly move routes into express.Router() instances (covered in the Express Router lesson) grouped by resource, users.routes.js, orders.routes.js, and mount them under a common prefix.

Group related routes by resource, not by HTTP method.
Mount grouped routers under a prefix: app.use('/api/users', userRouter).
Keep route files focused on wiring, move logic into controllers/services.

Common Mistakes

Placing a parameterized route (/users/:id) before a literal route (/users/new), silently breaking the literal one.
Defining the same method and path twice, only the first registered handler ever runs.
Using app.get() for a route that actually creates or mutates data, breaking REST conventions.
Forgetting the leading slash in a path string.

Key Takeaways

Routes pair an HTTP method with a path and one or more handler functions.
Express matches routes in registration order and stops at the first match.
Literal paths should be registered before similar parameterized paths.
As an app grows, group routes into express.Router() modules instead of one giant file.

Pro Tip

When two routes could match the same URL, run app.get('/users/new', ...) mentally against app.get('/users/:id', ...) and ask which one Express would hit first, order bugs like this are extremely common.