Browser Components + Python vs. JavaScript Execution Model + Role of JavaScript in Web Applications

Browser Engine

It coordinates the flow of information between the user interface, rendering engine, and other browser components

Rendering Engine:

Interprets HTML and CSS to display the page (e.g. Blink in Chrome, Gecko in Firefox)

JavaScript Engine

Executes JavaScript code (e.g., V8 in Chrome). This is where our app.js runs!

Networking Component:

Handles all communication with web servers (HTTP/HTTPS requests)

User Interface (UI):

The visible parts, like the address bar, back/forward buttons, and tabs

Browser Storage:

Mechanisms for websites to store data on your computer. This is a critical area for security vulnerabilities

Python:

• Typically synchronous

• Script → interpreter → process

• Blocking by default

JavaScript

• Event-driven

• Single-threaded event loop

• Non-blocking I/O

• Async by design (callbacks, promises)

What JavaScript actually does in the browser:

• Executes inside the user’s environment

• Manipulates the DOM (HTML + CSS)

• Handles user input and events

• Communicates with servers (fetch/AJAX)

• Enforces some client-side logic (but never trust it)