Dealing with CORS in your express app

What is CORS and how do you deal with it in your express app? Express, is a popular open source back end web application framework for Node.js. CORS stands for cross origin resource sharing, it is a mechanism that allow restricted resources on a web page to be requested from another domain outside the domain from which the first resource was served. CORS is implemented in modern browsers to prevent the browser from making a request to another website. When working with applications where the Front-end is separate from the backend CORS needs to be implemented on the backend otherwise you get a CORS error, the Cross-Origin Resource Sharing standard works by adding new HTTP headers that let servers describe which origins are permitted to read that information from a web browser. To implement CORS in your express app you need to install the cors NPM package npm install cors once installed add it to your express app

//index.js
const express = require('express');
const cors = require('cors');

const app = express();
const port = 3030;

//cors is enabled through out the entire app
app.use(cors());

app.get('/users', (request, response, next) => {
    res.json({info: 'cors is enabled'})
});

app.listen(port, () => {
    console.log(`App is running on ${port}`)
});

the above code would enable cors for all routes in your app, but what if you only want cors enabled for specific routes? we do this by adding cors to that particular route.

//index.js
const express = require('express');
const cors = require('cors');

const app = express();
const port = 3030;

//cors is enabled on this route
app.get('/users', cors(), (request, response, next) => {
    res.json({info: 'cors is enabled for this route'})
});

app.listen(port, () => {
    console.log(`App is running on ${port}`)
});

CORS is a security mechanism implemented to prevent one of the most common cyber attack: cross-site request forgery, where a malicious website attempts to take advantage of the browser's cookie storage system. in this article we've seen how to add CORS headers into our express app using the cors NPM package, we've also seen how to add cors to specific routes within our express app.