"I Built a Web Browser from Scratch in 42 Days — No Libraries, Just Node.js"

#javascript #beginners #programming #computerscience

I Built a Web Browser from Scratch in 42 Days

42 days ago I made a decision.

I wanted to understand how the internet actually works. Not just use it. Not just build on top of it. Actually understand it — at the wire level.

So I started building a web browser from scratch. In Node.js. No external libraries. Every line written by hand.

I called it Courage.

What Courage can do today

...

Parse URLs into protocol, host, port, path
Open raw TCP and TLS connections
Build and send HTTP GET requests
Parse HTTP responses including chunked encoding
Tokenize raw HTML character by character
Build a DOM tree using a stack
Match CSS rules to DOM nodes
Calculate layout (x, y, width, height) for every element
Paint rectangles and text on a Canvas using Electron
Execute JavaScript via eval()
Navigate with back, forward, reload
Multiple tabs with independent history
Render real websites — today it rendered Wikipedia

What I learned

Before this project I knew how to use the web. Now I understand it.

TCP handshakes aren't magic. HTTP is just text. HTML is just tokens. CSS is just rules. A browser is just a pipeline.

Every abstraction that used to feel like magic now makes complete sense.

The most surprising thing — a layout engine is just two passes over a tree. Width flows down from parent to child. Height bubbles up from child to parent. That's it. That's what every browser does.

The hard days

Day 9 — built a DOM tree using a stack. Failed 6 times before it clicked.

Day 21 — layout engine born. Took 3 days to get width and height right.

Day 42 — fixed a bug where CSS inside style tags was breaking the entire DOM tree because my tokenizer treated > in CSS selectors as HTML tag endings.

Every bug taught me something real.