Routing: Tables and Dynamic Paths

From if-chains to a routing table

The if-chain from lesson 3-1 works, but at 30 routes it becomes a wall. Real routers use a routing table: a data structure mapping method + path to a handler function.

const routes = {
  "GET /hello": () => "Hello!",
  "POST /orders": () => "Order placed",
};

Looking up a route is now one line: build the key, check the table. Adding a route is adding a line of data, not more branching logic. This "replace code with data" move is one of the most useful habits in backend work.

Dynamic segments: /users/:id

Every web framework supports path patterns like /users/:id. The :id part is a dynamic segment: it matches any value in that position and captures it as a param.

The matching algorithm is honest, simple string work:

1. Split both pattern and path on /.
2. If they have different lengths, no match.
3. Walk the pieces together. A piece starting with : always matches and records params[name] = value. Any other piece must be equal, or there is no match.

So /users/:id vs /users/42 gives { id: "42" }, and /users/:id vs /orders/42 fails at piece one. Params are always strings, converting "42" to a number is your job later. Now build it, this function sits inside every framework you will ever use.