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27th March, 2023

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How to Use Cors in Node.JS Express

Cross-origin resource sharing (CORS) is a mechanism that allows restricted resources on a web page to be requested from another domain outside the domain from which the first resource was served. A web page may freely embed cross-origin images, stylesheets, scripts, iframes, and videos.

Why is CORS needed?

The same-origin policy is a security policy enforced on client-side web applications (like web browsers) that restricts how these applications can communicate with each other.

Under the same-origin policy, a web browser permits scripts contained in a first web page to access data in a second web page, but only if both web pages have the same origin. An origin is defined as a combination of URI scheme, hostname, and port number.

How does CORS work?

When a browser receives a request for a resource from a different origin, it first sends a request to the server to check if the server gives permission for the browser to access the resource.

This request is called a preflight request.

The server can specify which origins are allowed to access the resource by setting the Access-Control-Allow-Origin header.

How do I use CORS in Express?

You can use the cors middleware in Express to enable CORS.

To use the cors middleware, you need to install the cors module.

npm install cors

Then, you can add the cors middleware to your Express app.

var express = require('express');
var cors = require('cors');

var app = express();

app.use(cors());

app.get('/', function (req, res) {
  res.send('Hello World');
});

app.listen(3000);

Conclusion

CORS is a mechanism that allows restricted resources on a web page to be requested from another domain outside the domain from which the first resource was served.

The cors middleware can be used in Express to enable CORS.

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