What happens when you type a URL into a browser and hit enter?

JavaScript

Solution

I would recommend you to structure your answer like a pyramid: start with a quick summary, then elaborate on the steps, and be prepared to go deeper on any point. However, I would not expect them you to go deeper into each step.

Step 1: 30 Second summary

At a high level, the browser first needs to find the server's address on the internet. It does this by converting the URL you typed into an IP address through a process called DNS lookup. Once it has the address, it establishes a secure TCP connection with the server and sends an HTTP request asking for the website. The server processes that request and sends back an HTTP response containing the site's content. Finally, the browser takes that content, primarily HTML, CSS, and JavaScript, and renders it into the visual page we see

Why this works: You've covered all major milestones (DNS, TCP, HTTP, Rendering) in a single, coherent paragraph. You've proven you have the map before you start describing the journey.

Step 2: Detailed, Step-by-Step Walkthrough

• First, the DNS Lookup: The browser needs to translate the domain name, like google.com, into an IP address. It first checks its cache—then the OS cache, router cache, and ISP cache. If it's not there, it initiates a recursive DNS query to find the authoritative name server holding the IP.
• Next, the TCP/IP Connection: With the IP address, the browser opens a TCP connection to the server. This is done via the TCP three-way handshake: the browser sends a SYN packet, the server responds with SYN-ACK, and the browser confirms with an ACK. Now, a reliable connection is established.
• Then, for security, the TLS Handshake: Since most sites today use HTTPS, a TLS handshake happens next to encrypt the connection. The browser and server negotiate encryption algorithms, the server provides its SSL certificate to prove its identity, and they securely generate a shared session key for encrypting all future communication.
• Now we send the HTTP Request: The browser, now with a secure connection, sends the HTTP request. This contains a request line (like GET / HTTP/1.1), headers (with information about the browser, cookies, etc.), and an optional body.
• The Server Sends the HTTP Response: The server receives the request, finds the necessary resources, and sends back an HTTP response. This includes a status code (like 200 OK), response headers (like Content-Type), and the body, which is the HTML code for the page.
• Finally, the Browser Renders the Page: The browser starts by parsing the HTML to build the DOM tree. When it encounters links to CSS or JavaScript, it repeats the request process to fetch them. It parses CSS to build the CSSOM tree. The DOM and CSSOM are combined into a Render Tree. The browser then performs Layout (calculating where everything goes) and Paint (drawing the pixels on the screen). JavaScript is executed, which can modify the DOM and make the page interactive."