Explanation of how a web browser receives data, processes it, and displays a webpage, including DNS resolution, TCP handshake, caching, DOM construction, and WebSocket communication.

The browser sends a request to a DNS server to translate the domain name into an IP address.
If the domain uses a Content Delivery Network (CDN), the DNS server may return the IP address of the nearest CDN server to optimize performance.

The browser inspects its local cache to determine if the requested resources are already stored:
- Valid Cache: If cache headers, such as Cache-Control or Expires, indicate that the resource is still fresh, the browser loads the resource directly from the cache without contacting the server.
- Expired Cache: If the cache is stale, the browser sends a conditional HTTP request to the server to check if the cached resource is still valid.

The server sends the requested resources (e.g., HTML, CSS, and JavaScript files) in small packets over the established connection.
Each packet contains a fragment of the requested file.

The browser receives the packets and reconstructs the complete files, including HTML, CSS, and JavaScript.

The browser parses the HTML file to build the DOM tree (Document Object Model), which represents the page’s structure.
The browser also parses CSS to build the CSSOM tree (CSS Object Model), which defines the page’s styles.

The browser combines the DOM tree and CSSOM tree into a Render Tree, which determines the visual elements of the page and their styles.
During the layout phase, the browser calculates the size and position of each element on the screen.

The browser paints the visual representation of the page onto the screen, rendering elements such as text, images, and background colors.
For pages with complex layouts, the browser performs compositing, which divides the page into layers for efficient rendering.

As the browser parses the HTML, it may encounter references to additional resources (e.g., images, videos, CSS files, JavaScript files).
The browser sends HTTP requests for these resources and downloads them using persistent TCP connections when possible.

If the page includes JavaScript, it can make API calls (e.g., using fetch or XHR) to request additional data from the server.
The browser processes the returned JSON data and uses it to update the page’s DOM dynamically.

For websites that use server-side rendering (SSR), the server pre-renders the page, including all necessary data, and sends the complete HTML to the browser.
This reduces the need for additional API calls to load initial content.

If the website uses WebSockets, the browser establishes a persistent connection with the server after the HTTP handshake.
This connection allows the server to send real-time updates, such as notifications or live chat messages, directly to the browser without requiring additional HTTP requests.

The browser begins displaying the page as soon as enough resources (e.g., HTML and CSS) are loaded and processed:
- Initial Render: The browser displays visible content as soon as possible, even if some resources (e.g., images or JavaScript) are still loading.
- Dynamic Updates: Additional resources, lazy-loaded assets, or API data may be loaded in the background to enhance the page after the initial render.

mattfsourcecode/browser-data-reception-and-rendering.md