Routing

Learn simple URL routing logic.

Routing

Routing means giving different responses based on the request path (req.url). The simplest way is checking the path with if conditions.

Example: if (req.url === "/") { res.end("Home"); } else if (req.url === "/about") { res.end("About"); } else { res.end("Unknown"); }. Here req.url gives the request path; each path produces a different response. The else branch provides a fallback for unknown paths. This is a simplified version of what frameworks like Express do behind the scenes; frameworks match the path with a more organized table.

Unknown paths

In routing it is good practice to always keep an else branch. This branch gives a fallback response for unmatched paths; this way no request hangs.

Example: if (req.url === "/") { res.end("Home"); } else { res.end("Unknown path"); }. A request to /about gets Unknown path. Usually unknown paths also set a 404 status: res.statusCode = 404; then res.end("Not found"). This clearly tells the user the path is invalid. statusCode is the response's HTTP status code; 200 means success, 404 means not found.

Exercise Write two-path routing

Import the http module. Create a server with createServer. Inside the handler check req.url: if "/" call res.end("Home"), otherwise res.end("Unknown"). The ready-made code below starts the server and sends a request to "/".

Show example solution

const http = require("http");
const server = http.createServer((req, res) => {
  if (req.url === "/") { res.end("Home"); }
  else { res.end("Unknown"); }
});

server.listen(3000, () => {
  http.get("http://localhost:3000/", (res) => {
    let body = "";
    res.on("data", (c) => body += c);
    res.on("end", () => { console.log("Reply: " + body); server.close(); });
  });
});

Test yourself

Which property is basic routing based on?
```
if (req.url === "/x") { ... }
```
- req.method
- res.end
- req.url
- server.listen
Show answer

req.url — req.url gives the request path; routing uses it.
Match each path to its response

"/"

Home
"/about"

About
else

Unknown
req.url

Request path

Complete the routing condition

if (req.____ === "/") { res.end("Ana sayfa"); }

Show answer

if (req.url === "/") { res.end("Ana sayfa"); }

Next lesson: JSON response

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