How Does a Web Browser Load and Execute a Web Page\'s Components?

Understanding the Load and Execution Sequence of a Web Page

When a browser encounters a web page, it initiates a sequence of events to load and execute its various components. This process can be understood as a series of steps:

1. HTML Parsing:

• The browser downloads the HTML document.
• It begins parsing the HTML, creating a Document Object Model (DOM) that represents the page structure.

2. Resource Loading and Execution:

• As the parser encounters external resources (e.g., CSS, JavaScript), it requests and downloads them.
• CSS Loading: CSS files are downloaded and parsed, and styles are applied to the DOM.
• Inline JavaScript: JavaScript code within <script> tags is parsed and executed.</script>
• External JavaScript: External JavaScript files are downloaded, parsed, and executed.

3. Image Loading:

• Images specified in tags are requested and downloaded, becoming part of the DOM.

4. Document Ready:

• Once all resources are loaded and the DOM is complete, the document.readyState property becomes "complete" and the "DOMContentLoaded" event is fired.

5. JavaScript Execution after Document Ready:

• Any JavaScript code within $(document).ready() blocks or that relies on the DOM being complete will execute at this stage.

6. Page Rendering:

• The page is rendered by combining the DOM, CSS styles, and images.
• Elements are displayed based on their positioning and styles.

7. User Interaction:

• The page responds to user interactions, such as clicking or entering text, through JavaScript event handlers.

Example Sequence:

For the sample page provided, the load and execution sequence would be roughly as follows:

1. HTML parsing
2. Loading and parsing jQuery.js
3. Loading and parsing abc.js
4. Loading and parsing abc.css
5. Parsing internal
6. Parsing internal JavaScript
7. Loading abc.jpg
8. Loading and parsing kkk.js
9. Document ready
10. Execution of $(document).ready block (change src of #img to kkk.png)
11. Page rendering and display

Additional Notes:

• Resource loading may be asynchronous, occurring in parallel to HTML parsing.
• Browser-specific settings may affect the order and timing of these steps.
• External resources may be cached, influencing load times and execution order.

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