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Introduction: As we enter a website's domain in the URL and hit enter, we embark on a fascinating journey through the inner workings of the World Wide Web. In this article, we'll take a closer look at the process that unfolds behind the scenes, as seen through the eyes of a frontend engineer. From the moment a user initiates a request to the delivery of content with HTML and CSS, let's explore the journey of content delivery on the web.
User Request and DNS Resolution: When a user enters a website domain in their browser's address bar and hits enter, the browser sends a request to a Domain Name System (DNS) server. The DNS server maps the domain name to an IP address, allowing the browser to locate the server hosting the website.
Establishing a Connection: Once the IP address is obtained, the browser establishes a connection with the web server using the Hypertext Transfer Protocol (HTTP) or its secure counterpart, HTTPS. This connection enables the browser to request the website's content.
Server-Side Processing: Upon receiving the request, the web server processes it and retrieves the requested resources. This can include HTML files, CSS stylesheets, JavaScript files, images, and other assets necessary to render the webpage.
Sending HTML Response: The web server constructs an HTML response containing the requested content and sends it back to the browser over the established connection. The HTML response forms the foundation of the webpage and provides the structure and content.
Parsing HTML: As the browser receives the HTML response, it begins parsing the document from top to bottom. The parser interprets the HTML tags, elements, and attributes, and constructs a Document Object Model (DOM) tree representing the webpage's structure.
Fetching CSS: While parsing the HTML, the browser encounters references to external CSS stylesheets. It initiates additional requests to the server to fetch these CSS files.
Applying CSS Styles: Once the CSS stylesheets are downloaded, the browser's rendering engine combines them with the parsed HTML to create a Render Tree. The Render Tree represents the final visual representation of the webpage, incorporating the styles defined in the CSS.
Rendering the Page: With the Render Tree in place, the browser's rendering engine computes the layout of the webpage, positioning elements on the screen according to the defined styles. It then paints the pixels on the screen, bringing the webpage to life visually.
Executing JavaScript: If the webpage includes JavaScript code, the browser executes it after the rendering process. JavaScript can manipulate the DOM, handle user interactions, fetch additional data, and add interactivity to the webpage.
Content Display: Once the rendering and JavaScript execution are complete, the browser displays the fully rendered webpage to the user. Images, videos, and other media content referenced in the HTML are fetched and displayed within the appropriate elements.
Conclusion: From the moment a user enters a website's domain in the URL until the content is delivered and rendered on the screen, a frontend engineer plays a crucial role in ensuring a smooth and engaging web experience. By understanding the process behind content delivery, we gain insights into the intricate mechanisms that power the modern web, making it an exciting field for frontend engineers to explore and innovate within.