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Biswas Prasana Swain
Biswas Prasana Swain

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How Web Browsers Work: A Simple Guide to Loading and Displaying Web Apps

#webdev #webperf #frontend #browser

Ever wondered what happens inside a web browser when you open a web app? It's like a magic show where many things happen behind the scenes. Let's break it down step-by-step and see how all the components of a web browser work together to make a website appear on your screen. We'll use some simple pseudocode to make it easier to understand.

1. The Web Browser Basics

A web browser is a tool that lets you view and interact with websites. Popular browsers include Chrome, Firefox, Safari, and Edge. Think of it as a magic box that turns web code into something you can see and use.

Here are the main parts of a web browser:

  1. User Interface (UI): This is what you see—the address bar, tabs, buttons, and the content area.
  2. Browser Engine: It acts as the core of the browser, facilitating communication with the components.
  3. Rendering Engine: This part takes the code and turns it into what you see on your screen.
  4. Networking: Handles communication between your browser and web servers.
  5. JavaScript Engine: Runs scripts that make websites interactive.
  6. UI Backend: Interacts with OS APIs to actually draw on screen.
  7. Data Storage: Keeps track of cookies, local storage, and other data.

2. Loading a Web Page

Let’s see how these parts work together to load and display a web app. Imagine you want to visit example.com. Here’s what happens in pseudocode:

Step 1: User Requests the Web Page 

User types "example.com" into the address bar Browser Engine checks if it's already in cache (saved copies) If not cached: Browser Engine sends a request to the server via Networking Component
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Step 2: Networking Component 

Browser Engine prepares a request for Networking Component Send HTTP request to server for "example.com" Waits for server to respond
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Step 3: Server Response 

Server receives request Looks up the requested page Sends back HTML code Browser Engine receives HTML code & sends to Rendering Engine
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Step 4: Rendering the HTML 

Rendering Engine starts processing HTML code Parses HTML into a Document Object Model (DOM) DOM represents the structure of the page (elements like headers, paragraphs, etc.)
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Step 5: Loading CSS (Styling) 

Finds CSS files linked in the HTML Requests these CSS files Receives CSS code Applies CSS styles to the DOM
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Step 6: Loading JavaScript 

Finds JavaScript files linked in the HTML Requests these JavaScript files Receives and executes JavaScript code JavaScript can manipulate the DOM and CSS
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Step 7: Displaying the Page 

Rendering Engine paints the styled DOM on the screen UI Backend draws content Interactivity is added by JavaScript User sees the web page
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Step 8: User Interaction 

User interacts with the page (clicks, types, etc.) Browser Engine receives interactions JavaScript Engine processes interactions Updates the DOM as needed Refreshes the display
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3. Keeping Data

Throughout this process, your browser might store some data:

Browser stores cookies, local storage, session data Data is used for personalization, remembering login info, etc.
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Summary

Diagram of how a web browser loads and displays a web app

Image courtesy of BrowserStack.

Here’s a quick recap of how a web browser works to load and display a web app:

  1. User Request: You type a URL, and the browser sends a request.
  2. Networking: Communicates with the server to get the web page.
  3. Rendering: Processes HTML into a DOM and applies styles.
  4. JavaScript: Adds interactivity and updates the page.
  5. Display: Shows the final result on your screen.
  6. Interaction: Handles user actions and updates the page as needed.
  7. Data Storage: Keeps track of important data for later use.

And that's how your web browser turns code into the web apps you use every day!

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