How does CORS work internally in JavaScript?

CORS, or Cross-Origin Resource Sharing, is a security feature implemented in web browsers to prevent malicious websites from making requests to a different origin (domain, protocol, or port) than the one that served the web page. When a web application attempts to make a cross-origin request, the browser sends an HTTP request including the Origin header to the server to check if the request is allowed. If the server supports CORS, it will respond with specific headers that grant permission for the browser to proceed with the request.

Internally, the CORS mechanism checks for permitted origins, HTTP methods, and headers, providing granular control over what resources can be shared with which web applications. If the server's response includes the appropriate CORS headers, the browser will allow the web application to access the response data.

Here’s a simple example of how CORS works in JavaScript:

// Example of a fetch request in JavaScript fetch('https://api.example.com/data', { method: 'GET', headers: { 'Content-Type': 'application/json' }, }) .then(response => { if (!response.ok) { throw new Error('Network response was not ok'); } return response.json(); }) .then(data => console.log(data)) .catch(error => console.error('There was a problem with the fetch operation:', error));

CORS Cross-Origin Resource Sharing JavaScript HTTP Security Web Development

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