Just Learn Code

Mastering CORS: Best Practices for Secure and Efficient Web Development

Cross-Origin Requests (CORS) are crucial for web development. However, it can be challenging to manage different hosts, protocols, and ports.

The primary goal of this article is to make CORS more accessible by breaking down what qualifies as cross-origin requests, setting up CORS support, and handling cross-origin requests in Express. As a web developer, knowing how to handle CORS is an essential skill that can enhance your development process.

Understanding Cross-Origin Requests

CORS is a protocol that allows web servers to share resources with different origins. An origin refers to the unique URL derived from a combination of the protocol, host, and port.

In a simplified explanation, if the protocol, host, and port are the same, two webpages share the same origin. However, if one or more are different, this is considered cross-origin.

Cross-origin requests can be hazardous as they allow a malicious website to interact with trusted websites, making it possible for them to steal user information and perform unintended operations. However, not all cross-origin requests are unsafe.

Some requests are safe since they do not allow changes to the data.

Setting Up CORS Support

To understand CORS support set up, it is essential to know that CORS includes two types of HTTP requests: Simple requests and preflight requests. Simple requests are requests that do not require preflight checks.

On the other hand, preflight requests are requests that require preflight checks. There are several ways of implementing CORS support, such as creating a custom server using languages such as Java, Python, or Ruby, or by using the appropriate plugins that support CORS.

A plugin, commonly known as a cors plugin, can help in adding a proper cross-origin request support. The most typical request in CORS is the preflight request, which uses the OPTIONS method.

OPTIONS requests help gather information about cross-origin requests and help the server determine if the request is safe to proceed. The Access-Control-Allow-Origin header ensures that only safe requests proceed, while other requests are blocked.

Handling Cross-Origin Requests in Express

Express is a popular server-side web application framework that enables Node.js to create web applications. Setting up CORS in Express can be done by using the ‘cors npm’ module.

Once installed, wrap the express app with the cors middleware to enable cross-origin requests on all routes.

One of the most crucial parts of setting up CORS in Express is to ensure that the Access-Control-Allow-Origin, Access-Control-Allow-Methods, and Access-Control-Allow-Headers headers are present in the response.

These headers tell the browser which requests are safe to proceed. If these headers are missing, the browser will block the request.

If you need to handle preflight requests, you will need to create a specific route that handles the OPTIONS request method. Once the preflight request is completed, the next middleware function is called and is expected to send a response.

Creating a Proxy

Creating a proxy with cross-origin requests can help in working around CORS. It involves setting up a front-end framework to send its requests to a backend server that acts as a proxy between the client and the server.

Once a proxy is created, requests from the browser automatically go through the proxy server, bypassing the CORS restrictions.


Cross-origin requests are essential for web development in the current digital age. However, managing the different aspects of cross-origin requests can be challenging.

Using a cors plugin for the server, handling preflight requests in Express, and creating a proxy are some of the ways to handle cross-origin requests. As a web developer, understanding CORS is vital to enhance your development process.

With the information provided in this article, handling cross-origin requests will no longer be a challenging task.

Best Practices for CORS

Cross-Origin Resource Sharing (CORS) is a vital aspect of web development that allows sharing of resources between different origins. However, CORS can pose security risks and negatively impact performance, making it crucial to implement best practices for safer and more efficient web development.

Security Risks of CORS

CORS can pose security risks as it enables cross-site scripting (XSS) and cross-site request forgery (CSRF) attacks. These attacks allow malicious actors to steal sensitive data, such as user credentials and credit card numbers.

To mitigate these risks, it is crucial to restrict access to sensitive data by allowing only authorized domains to access such data. To ensure secure CORS, it is essential to use the same-origin policy, which is a mechanism for preserving security by restricting the resources that a web page can fetch from different origins.

For example, a script hosted on www.example.com cannot read or write any data from a different origin such as www.adversary.com. Another best practice is to limit the amount of data that is exposed through cross-origin requests.

The server should be programmed to allow only essential data-sharing between different origins while limiting access to sensitive information.

Impact on Performance

Cross-origin requests affect performance and cause additional overhead, resulting in delays and latency. Sending excessive requests can result in server overloads, which can negatively affect website performance.

Higher latency results in slower load times, which can frustrate users and drive them away from your website. To minimize latency and improve website performance, reduce the number of cross-origin requests and implement caching mechanisms to reduce server requests frequency.

Caching mechanisms can be used to store responses and requests to reduce network congestion. Implementing server-side caches will reduce the amount of data transferred from the server to the client, consequently reducing latency and improving website performance.

Mitigating Security and Performance Risks

Mitigating security risks in CORS can be achieved by validating the source of the request and ensuring that only authorized domains can access sensitive data. Additionally, it is crucial to specify allowed methods and headers explicitly.

By configuring specific headers, it is possible to verify the origin of the request and block any unauthorized access. Using the Access-Control-Request-Headers header, it is possible to specify the headers that are required by the resource.

Preflight caching is another best practice to improve performance. Preflight caching enables clients to cache responses to preflight requests, eliminating the need for the server to process the request repeatedly.

By disabling preflight requests, a server can significantly speed up response time and reduce overhead. Another best practice for mitigating server overload is to use HTTP/2 server push, which enables the server to proactively push frequently used resources to the client.

This approach reduces the total number of requests, reduces latency, and minimizes the number of connections between the client and the server.


CORS is an essential protocol for web development that enables the sharing of resources between different origins. However, it poses security risks and negatively impacts website performance.

Implementing security best practices, such as limiting access to sensitive data, reducing cross-origin requests, enabling caching mechanisms, and mitigating server overloads, are crucial to ensure secure and efficient web development. By following these best practices, web developers can create safer and higher-performing web applications.

Overall, the best practices for Cross-Origin Resource Sharing (CORS) are essential for creating secure and efficient web development. This protocol can pose security risks and negatively impact website performance if not correctly implemented.

However, implementing security measures such as restricting access to sensitive data, reducing cross-origin requests, enabling caching mechanisms, and using HTTP/2 server push can significantly improve website performance while staying secure. Web developers must prioritize implementing these best practices to create safe, efficient, and high-performing web applications.

Popular Posts