How to setup Regex for ExpressJS router url in Node.js ?

ExpressJS Router is a class that acts as a middleware to provide route handling or determining how an application responds to a client requests, of various HTTP methods, to a particular URI.

Creating Express App and Installing Module:

Step 1: Create package.json using the following command:

npm init

Step 2: You can visit the link Install Express to see how to install the express module. You can install this package by using the command :

npm install express

Step 3: Create app.js, params.js, and routes.js files in the view folder. The project directory will look like this:

Project Structure

Setup Regex in URL:

We can easily set up Regex for our Express Router by following these two points:  

• To make our route match with a particular regular expression, we can put regex between two forward slashes like this /<routeRegex>/
• Since every route contain /, so wherever we have to use / inside Regex, use a backslash \ / before it.

Example: In the following code, we are setting up regex, for when HTTP get request is received to route /home, a response Homepage is rendered to the client. 

router.get(/\/home/ , (req,res)=>{
    res.send('Homepage');
)

Now create a routes.js file that will contain different requests for different routes using Regex. 

routes.js

// Requiring module
const express = require('express');
const router = express.Router();

// Route which matches /abc or /adc
router.get(/\/a[b|d]c/, (req, res) => {
    res.send("<h1>Route First</h1");
})

// Routes that matches /a(any single digit)/
// followed by 2 times c or 3 times c or
// /a(any single digit) / followed by 2
// times c or 3 times c
router.get(/\/a[0-9]\/c{2,3}/, (req, res) => {
    res.send("<h1>Route Second</h1");
})

// Routes that ends with /Hello followed by
// a letter in [a-z] any no. of times and
// ends with "OK"
router.get(/^\/Hello[a-z]*OK$/, (req, res) => {
    res.send('<h1>Route Third</h1>')
})

// Routes that must end with string "Hello"
// and can have any no. of any character
// before that
router.get(/\/*Hello$/, (req, res) => {
    res.send('<h1>Route Fourth</h1>')
})

module.exports = router;

Setting up Regex in URL parameters:

To set up Regex for URL parameters, we can provide regex inside parenthesis just after the name of the parameters. In the following file, we have implemented Regex for URL parameters.

params.js

// Requiring module
const express = require('express');
const router = express.Router();

// Setting up regex for name and contact parameters
router.get('/user/:name([a-zA-Z]+)/:contact([6-9][0-9]{9})', (req, res) => {
    const name = req.params.name;
    const contact = req.params.contact;
    res.send({
        "username": name,
        "contact": contact
    })
})

module.exports = router;

app.js

// Requiring modules
const express = require('express');

const app = express();
const router = express.Router();

const route = require('./routes');
const param = require('./params');

// Using routers as middleware to
// use route.js and params.js
app.use('/', route);
app.use('/', param);

// Starting server on port 8000
app.listen(8000, () => {
    console.log("Server is listening on port 8000");
})

Step to run the application: Run the app.js file using the following command.

node app.js

Output:

• Showing the functioning of all the routes defined in the routes.js file.

Execution of routes.js

• Showing the functioning of the routes defined in the params.js file.

Execution of params.js