A web page rests on three complementary languages. Understanding what each one does makes JavaScript’s role immediately clear.

The three pillars of the web

  • HTML — structure and content (headings, paragraphs, images).
  • CSS — appearance and layout (colours, fonts, positioning).
  • JavaScript — behaviour and interactivity.

If a page were a house, HTML would be the walls, CSS the paint, and JavaScript the electricity: it is what switches things on, reacts and makes them move. Thanks to it, a button can open a menu, a form can check what has been typed, or a page can load new data without reloading.

JavaScript runs directly in the visitor’s browser: the end user has nothing to install. It is the only language every browser understands natively, which makes it unavoidable.

Key takeaway: HTML structures, CSS styles, JavaScript animates. It is what makes a page interactive.

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