Routing

Routing refers to how an application’s endpoints (URIs) respond to client requests.

You define routing using methods of the Express app object that correspond to HTTP methods; for example, app.get() to handle GET requests and app.post to handle POST requests.

Routing Methods

A route method is derived from one of the HTTP methods, and is attached to an instance of the express class.

The following code is an example of routes that are defined for the GET and the POST methods to the root of the app.

// GET method routeapp.get("/", (req, res) => {    res.send("GET request to the homepage");});// POST method routeapp.post("/", (req, res) => {    res.send("POST request to the homepage");});

Add Route To Our App

In Our express app, we will add a route that will be responsible for handling requests to our Dog resource

Create a new folder called routes in the root of our project and add two files: index.js and dog.js.

mkdir routes && touch routes/index.js && touch routes/dog.js

In our index.js file, we need to add the following code:

const router = require("express").Router();router.use("/dogs", require("./dog"));module.exports = router;

Inside the dog.js file, we need to add the following code:

const router = require("express").Router();// Used to get all dogsrouter.get("/", (req, res) => {    res.send("Hello from dog");});// Used to get a dog by idrouter.get("/:id", (req, res) => {    res.send(`Hello from dog ${req.params.id}`);});// Used to create a new dogrouter.post("/", (req, res) => {    res.send("POST request to the dog");});// Used to update a dogrouter.put("/:id", (req, res) => {    res.send(`PUT request to the dog ${req.params.id}`);});// Used to delete a dogrouter.delete("/:id", (req, res) => {    res.send(`DELETE request to the dog ${req.params.id}`);});module.exports = router;

Mock Database

In a real application, we would likely have a database that stores our data.

We can use a mock database to simulate this database.

Inside the dog.js file at the top, we need to add the following code:

let dogs = [    {        id: 1,        name: "Fido",        breed: "Poodle",    },    {        id: 2,        name: "Spot",        breed: "Dalmation",    },    {        id: 3,        name: "Buddy",        breed: "Pug",    },];

Update Routes

Now that we have our routes defined, we need to update our route functions/methods to use the mock database.

// Used to get all dogsrouter.get("/", (req, res) => {    res.json(dogs);});// Used to get a dog by idrouter.get("/:id", (req, res) => {    const dog = dogs.find((dog) => dog.id === parseInt(req.params.id));    if (!dog) {        return res.status(404).send("Dog not found");    }    res.json(dog);});// Used to create a new dogrouter.post("/", (req, res) => {    let newDog = req.body;    newDog.id = dogs.length + 1;    dogs.push(newDog);    res.json(newDog);});// Used to update a dogrouter.put("/:id", (req, res) => {    const dog = dogs.find((dog) => dog.id === parseInt(req.params.id));    if (!dog) {        return res.status(404).send("Dog not found");    }    dog.name = req.body.name;    dog.breed = req.body.breed;    res.json(dog);});// Used to delete a dogrouter.delete("/:id", (req, res) => {    const dog = dogs.find((dog) => dog.id === parseInt(req.params.id));    if (!dog) {        return res.status(404).send("Dog not found");    }    dogs = dogs.filter((dog) => dog.id !== parseInt(req.params.id));    res.json(dog);});

Update Server.js File

Now that our dog resource is updated, we need to add our routes to our server.js file.

remove this from the server.js file:

// ...app.get("/", (req, res) => {    res.send("Hello World!");});// ...

Add the following code to the server.js right before calling the listen function:

app.use("/api", require("./routes"));

Test Our Routes

Restart the dev server and test the endpoints with a HTTP Client. An HttpClient can be used to send requests and retrieve their responses.

Send a GET request to http://localhost:3000/api/dogs. The repsonse should be a JSON array of all dogs.

[    {        "id": 1,        "name": "Fido",        "breed": "Poodle"    },    {        "id": 2,        "name": "Spot",        "breed": "Dalmation"    },    {        "id": 3,        "name": "Buddy",        "breed": "Pug"    }]