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

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

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

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

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.)

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

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

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

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

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.

Summary

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!