The Building Blocks of Web Development (HTML, CSS, JS) - How Browser Works?

The Building Blocks of Web Development (HTML, CSS, JS) - How Browser Works?

Sridhar Raj P Sridhar Raj P

Sridhar Raj P

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Published Jun 21, 2024
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Web development revolves around three core technologies: HTML, CSS, and JavaScript. These are the building blocks of the web. Here’s a detailed look at how each of these technologies contributes to web development and how browsers process and render them:

1. HTML (HyperText Markup Language)

HTML is the foundation of web pages. It defines the structure and content of a webpage.

  • Elements and Tags: HTML uses tags to create elements like paragraphs, headings, links, images, and more.
  • Attributes: Tags can have attributes that provide additional information, such as href for links and src for images.
  • Document Structure: An HTML document typically includes a <!DOCTYPE html> declaration, a <html> root element, a <head> for meta-information, and a <body> for content.

2. CSS (Cascading Style Sheets)

CSS is used to control the presentation and layout of HTML elements.

  • Selectors: CSS selectors identify HTML elements to apply styles to.
  • Properties and Values: CSS properties define specific styles (e.g., color, font-size, margin), and values assign those styles.
  • Cascading and Inheritance: Styles can cascade and inherit from parent elements, allowing for flexible and maintainable design.

3. JavaScript

JavaScript is a programming language that enables dynamic, interactive behavior on web pages.

  • Scripting and Interactivity: JavaScript can manipulate the DOM, handle events, validate forms, and interact with servers.
  • APIs: JavaScript interacts with various APIs for tasks like AJAX calls, geolocation, and local storage.
  • Libraries and Frameworks: JavaScript has a rich ecosystem of libraries (e.g., jQuery) and frameworks (e.g., React, Angular, Vue.js) that streamline development.

How Browsers Work with HTML, CSS, and JavaScript

Here’s an overview of how browsers process and render web pages using these technologies:

Step-by-Step Browser Process

  1. User Input: The user enters a URL or clicks a link.
  2. URL Processing and DNS Lookup: The browser processes the URL, performs a DNS lookup, and sends an HTTP request to the server.
  3. Server Response: The server responds with an HTML document, potentially including links to CSS, JavaScript files, and other resources.

HTML Processing

  1. HTML Parsing: The browser parses the HTML document to construct the DOM tree, representing the document structure as a hierarchical tree of nodes. Each HTML tag becomes a node in the DOM.

CSS Processing

  1. CSS Parsing: The browser parses the linked or embedded CSS to construct the CSS Object Model (CSSOM).The CSSOM and DOM are combined to create a render tree that includes only the nodes to be displayed, along with their computed styles.

JavaScript Processing

  1. JavaScript Execution:The browser’s JavaScript engine (e.g., V8 in Chrome, SpiderMonkey in Firefox) parses and executes JavaScript code. JavaScript can modify the DOM and CSSOM, potentially causing reflows (layout recalculations) and repaints (screen redraws).JavaScript may also fetch additional resources asynchronously (e.g., via AJAX).

Layout and Painting

  1. Layout (Reflow):
  2. Painting:

Reflows and Repaints

  1. Reflows and Repaints: Changes to the DOM or CSSOM can trigger reflows (layout recalculations) and repaints (updating the screen).Frequent reflows and repaints can affect performance, so minimizing them is crucial for a smooth user experience.

Interaction Between HTML, CSS, and JavaScript

  • HTML as Structure: HTML provides the structure and content of the web page.
  • CSS as Presentation: CSS defines how the HTML elements should be displayed.
  • JavaScript as Behavior: JavaScript enables dynamic interactions and functionality.

Understanding how browsers process and render HTML, CSS, and JavaScript helps developers optimize web performance and create responsive, interactive web applications. By leveraging these core technologies effectively, developers can build robust and engaging websites.

The Building Blocks of Web Development - How Browser Works?

Web browsers are essential tools for accessing and interacting with the World Wide Web. They function by retrieving, presenting, and traversing information on the internet. Here’s a breakdown of how browsers work, encompassing their main components and processes:

1. User Interface (UI)

The user interface is what users interact with directly. It includes:

- Address bar: Where users type URLs.

- Back and forward buttons: For navigation.

- Bookmarking options: For saving favorite websites.

- Reload/Refresh button: To reload the current page.

- Home button: Takes the user to the browser’s homepage.

- Tabs: Allows multiple pages to be open simultaneously.

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2. Browser Engine

The browser engine bridges the user interface and the rendering engine. It manages the rendering engine to display web content correctly.

3. Rendering Engine

This component is responsible for displaying the requested web page content on the screen. The process includes:

- Parsing HTML: Converts HTML into a Document Object Model (DOM) tree.

- Parsing CSS: Converts CSS into a render tree.

- Layout: Calculates the position and size of all elements on the page.

- Painting: Fills in the pixels on the screen.

Popular rendering engines include:

- Blink: Used by Chrome and Opera.

- WebKit: Used by Safari.

- Gecko: Used by Firefox.

4. Networking

The networking component handles all network calls, such as HTTP requests and responses. It retrieves resources like HTML documents, images, CSS files, and JavaScript files.

5. JavaScript Engine

Browsers contain a JavaScript engine that interprets and executes JavaScript code. This enables dynamic content and interactive features on web pages. Notable JavaScript engines include:

- V8: Used by Chrome and Edge.

- SpiderMonkey: Used by Firefox.

- JavaScript Core (Nitro): Used by Safari.

6. UI Backend

This is used for drawing basic widgets like combo boxes and windows. It exposes a generic interface that is not platform-specific, enabling the rendering engine to draw UI elements.

7. Data Storage

Browsers need to store various data locally, such as cookies, cache, local storage, and databases. This component handles all storage mechanisms used by the browser to store data on the user's device.

How Browsers Work: The Process

Here is a step-by-step outline of how browsers typically process and render a web page:

1. User Input: The user enters a URL in the address bar and presses enter.

2. URL Processing: The browser parses the URL to determine the protocol (usually HTTP or HTTPS) and identifies the domain name.

3. DNS Lookup: The browser sends a request to a DNS server to resolve the domain name to an IP address.

4. HTTP Request: The browser sends an HTTP request to the server located at the resolved IP address.

5. Server Response: The server processes the request and sends back an HTTP response, which includes the requested resource (HTML document).

6. HTML Parsing: The browser parses the HTML document to construct the DOM tree.

7. CSS Parsing: The browser parses the CSS to construct the render tree.

8. JavaScript Execution: If the HTML document includes JavaScript, the browser’s JavaScript engine executes it, which may modify the DOM or CSSOM.

9. Layout: The browser calculates the layout of the page, determining the position and size of elements.

10. Painting: The browser paints the pixels on the screen, rendering the web page visible to the user.

11. Reflows and Repaints: As JavaScript interacts with the page, it can trigger reflows (layout recalculations) and repaints (screen redraws).

Understanding these building blocks and processes provides insight into how web browsers operate and render web content efficiently.

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