Preventing cross-site scripting attacks

XSS attacks are client-side injection attacks where malicious scripts are injected into websites. XSS vulnerabilities are very dangerous, as they can compromise trusted websites.

In this recipe, we're going to demonstrate an XSS vulnerability and learn how we can protect against them.

Getting ready

In this recipe, we'll create an Express.js server that is vulnerable to an XSS attack. We must first create the vulnerable Express.js server:

1. Let's first create a directory to work in:

   $ mkdir express-xss
   $ cd express-xss
   $ npm init --yes

2. Now, we need to install express:

   $ npm install express

3. Create a file to store the Express.js server:

   $ touch server.js

4. Add the following to server.js. This will create a server that renders a simple HTML web page that is susceptible to an XSS attack:

   const express = require("express");
   const app = express();
   app.get("/", (req, res) => {
     const...