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Web & Networking Foundations · Foundational web concepts

How the Web Is Built: HTML, CSS, JavaScript, and the Client-Server Model

Learn the client-server model, HTML/CSS/JavaScript roles, and why browser-side code cannot be trusted for security.

Before we begin, here is exactly what you will be able to do by the end of this lesson.

By the end of this lesson, you will be able to:

  • Describe the client-server model and explain what happens during the request/response round-trip.
  • Identify the three languages every web page is built from — HTML, CSS, and JavaScript — and state the distinct role of each.
  • Explain what the DOM is and describe how CSS and JavaScript interact with it.
  • Distinguish between a static page and a dynamic page.
  • Classify browser-side and server-side responsibilities in the custom Responsibility Sorter.
  • Trace an HTTPS request from navigation through rendering with the HTTP Flow Walk-through.
  • Explain why client-side code cannot be trusted for security decisions, and why the server must independently re-validate everything it receives.

These outcomes are the foundation for every lesson that follows. When you are ready, send Continue.