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How the web actually works

KS4 · 30 minutes · Trace a request from URL to pixels.

Visual learning map for How the web actually works: observe, try, then explain. Trace a request from URL to pixels.
Visual learning map for How the web actually works: observe, try, then explain. Trace a request from URL to pixels.

Answer by: Type. You can change method or take a break at any time.

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Our learning goal

Trace a request from URL to pixels.

Your turn: Choose one thing you would like to understand by the end.

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My lesson notes & project
Full teaching script
  1. Today: How the web actually works. Our goal: Trace a request from URL to pixels.
  2. Take one idea at a time. Pause after each sentence; ask for repetition whenever you need it.
  3. You type a URL. DNS turns the name into an IP address. Your browser opens a TCP connection, negotiates TLS so the traffic is encrypted, then sends an HTTP request. The server answers with a status code and HTML. The browser parses that into a DOM tree, fetches CSS and JavaScript it references, builds the render tree, lays out boxes and paints. JavaScript can then mutate the DOM, and every mutation may cost another layout and paint — which is why heavy pages feel slow on cheap phones.
  4. Together: choose one example from the explanation and show how it works. What do you notice?
  5. Your turn: Open developer tools, load a site, and label every step in the network waterfall.
  6. Reflect: what made sense, and what would you like explained differently?
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