In this React 19 tutorial, I move from building UI that only displays data to UI that actually responds to users. Up to this point we’ve covered props, JSX, conditional rendering, lists, and styling, but none of that matters if your components can’t react to clicks, hovers, or keyboard input. So I create a simple CustomButton component and show the two-step process for event handling: define a function (like handleClick) and pass it to a special prop that starts with “on”, such as onClick. I also highlight a super common beginner mistake: calling the handler with parentheses. If you write onClick={handleClick()}, the function runs immediately during render and you end up passing undefined to onClick. What you want is onClick={handleClick} so React can call it later when the user clicks. From there, I show that React supports the usual events you’d expect (onChange, onSubmit, onMouseEnter, and so on), and I demonstrate the event object—event.target, clientX/clientY, and event.button. Finally, I show a really important detail: event handlers can access component variables and props because they’re defined inside the component. I use a local name variable and a text prop to render multiple buttons (Like and Bookmark) and log a custom message based on which button was clicked.