Events are actions that happen when a user interacts with the page - like clicking an element, typing in a field, or loading a page. The transform properties can be accessed in a variety of Donations to freeCodeCamp go toward our education initiatives, and help pay for servers, services, and staff. In this example, we want to trigger click event and make sure shift key is pressed when it happens. Events can be listened for by using addEventListener or inline methods such as onclick. Now try clicking the button and then the video: An alternative form of event propagation is event capture. On the other hand, mousedown and mouseup handlers may need event.button, because these events trigger on any button, so button allows to distinguish between right-mousedown and left-mousedown. Some browsers support automatic form data validation features, but since many don't, you are advised to not rely on those and implement your own validation checks. The video is inside the