To understand how you can make web pages interactive, you need to first grasp how the browser event system works. The browser constantly monitors various event sources—such as user actions (clicks, keystrokes, mouse movements), network responses, timers, and more. When something happens, the browser generates an event object that describes the action.

You can react to these events by attaching event listeners to DOM elements. An event listener is a function you provide that the browser will call when a specific event occurs on a specific element. The process begins with the user or another source triggering an event. The browser then places this event into an internal queue, managed by what is known as the event loop. The event loop ensures that all events are handled in the order they arrive, and that your code responds at the right time.

When the event loop processes an event, it checks if any event listeners are registered for that event type on the relevant DOM element. If so, your handler function is called with the event object as its argument. This is how you can respond to user input or other changes in your web application.