This demonstrates how a tab opened by a regular HTML link can be closed automatically. The link will be clicked, and then the click can be prevented by using a simple function called preventDefault()

linkElement.addEventListener("click", (e) => {
    e.preventDefault(); // Prevent the link from being clicked
})

and then, opening a new tab (using window.open) and closing it after a while. Users might think this is a link that takes them to the new page but it actually is a new window object made by JavaScript, when we got input from the user, we cancelled it and used it for another purpose.

linkElement.addEventListener("click", (e) => {
    e.preventDefault(); // Prevent the user from clicking the link
    tab = window.open("https://wikipedia.org"); // Open a new tab
    setTimeout(() => tab.close(), 2000); // Close the newly opened tab after 2 seconds
})

Kinda scary but fun at the same time.

This demonstrates how whatever you copy from a website can be modified, when you copy text, preventDefault() is called to prevent copying it, and clipboardData.setData() is used to modify the contents of the clipboard.

element.addEventListener("copy", (e) => {
  e.clipboardData.setData("text/plain", "Foo Bar"); // Use the event to copy something into the users clipboard
  e.preventDefault(); // Cancel the actual event.
})

This is why you should always be careful when you copy text from a website and paste it somewhere else.

JavaScript has access to lots of information regarding your browser and computer, this info is not very sensitive but can be easily used to uniquely identify a user. The navigator object contains a lot of info about the user's browser and computer without requiring the user's permission, here's an example. The most commonly used is navigator.userAgent, which returns the userAgent string of a user, which contains the name and version of the user's Operating System and browser.