What happens when you type a url in the browser address bar?

Have you ever wondered what happens behind the scenes when you type https://example.org in the browser address bar and press enter?

Here's a detailed breakdown of the process:

1. URL Parsing: The browser parses the entered URL to understand its components. These components include the protocol (e.g., HTTP or HTTPS), domain name (e.g., www.example.com), path (e.g., /page), and any query parameters (e.g., ?id=123).

2. DNS Resolution: The browser needs to resolve the domain name (e.g., www.example.com) to an IP address. The domain that is typed into the browser is the human readable version of the IP address. It checks its own cache to find the IP address associated with the domain if it has visited it before. If not found, it sends a DNS (Domain Name System) request to a DNS server to obtain the IP address.

3. Establishing a TCP Connection: Using the resolved IP address, the browser initiates a TCP (Transmission Control Protocol) connection with the web server hosting the requested website. This is basically the browser saying: Hello, I need this page or this resource. And these are my credentials. The TCP connection follows a three-way handshake process to establish a reliable connection.

4. Sending an HTTP Request: Once the TCP connection is established, the browser sends an HTTP (Hypertext Transfer Protocol) request to the web server. The request includes the HTTP method (e.g., GET, POST), the requested resource path, query parameters, headers (e.g., user agent, cookies), and more.

5. Server Processing: Upon receiving the HTTP request, the web server processes it. This typically involves interpreting the request, routing it to the appropriate application or server-side code, and generating an HTTP response.

6. Application Processing: If the requested resource requires server-side processing (e.g., dynamic content, database access), the server-side application handles the request. It may interact with databases, perform calculations, or retrieve data to generate the appropriate response.

7. Generating an HTTP Response: Based on the request, the server-side application generates an HTTP response. The response includes a status code (e.g., 200 for success, 404 for not found), headers (e.g., content type, caching directives), and the response body (e.g., HTML content).

8. Data Transfer: The server sends the generated HTTP response back to the browser over the established TCP connection. The response is broken into smaller packets for efficient transmission.

9. Rendering the Web Page: Upon receiving the response, the browser begins processing it. It first checks the response status code to determine if the request was successful. If successful, it reads the response headers to gather information such as content type and caching instructions.

10. HTML Parsing: If the response body is HTML, the browser starts parsing the HTML content. It builds a Document Object Model (DOM) tree, representing the structure and elements of the web page.

11. Resource Loading: While parsing the HTML, the browser encounters additional resources referenced in the HTML, such as CSS files, JavaScript files, images, and other assets. The browser starts loading these resources by sending additional HTTP requests to the server.

12. Rendering and Layout: As the browser fetches the resources, it progressively renders and displays the web page. It applies CSS styles to elements, executes JavaScript code, and arranges the elements on the page according to the layout rules.

13. Interaction and Event Handling: Once the web page is fully loaded and rendered, the browser allows user interaction. It handles user actions, such as clicking links or submitting forms by generating appropriate HTTP requests and initiating the process again from step 2.

This process, known as the HTTP request-response cycle, allows the browser to retrieve and display web pages from web servers. Each time you enter a URL and press enter, these steps are repeated to fetch and render the requested content, providing you with the web page you requested.