When you interact with a web page—by clicking a button, typing in a form, moving your mouse, or even when a page finishes loading—the browser detects these actions as events. Events are signals that something has happened, either as a result of user interaction, a system process, or custom logic defined in your code. Understanding events is fundamental to building interactive web pages, because they allow you to respond to what users do in real time.

There are several types of browser events:

• User events: triggered by user actions, such as clicks, key presses, mouse movements, or scrolling;
• System events: triggered by the browser or the environment, such as a page finishing loading, an image failing to load, or the browser window being resized;
• Custom events: triggered by your own code, allowing you to define and dispatch events for specialized behaviors.

Events are essential because they make web pages dynamic and interactive. Without events, a web page would be static: users could see content, but nothing would respond to their actions. By listening for and handling events, you can create rich user experiences where the page updates, reacts, and communicates with users as they interact with it.