how to make an event listener in javascript code example

Example 1: event listener javascript

const element = document.querySelector(".class__name");

element.addEventListener("click", () => {
	console.log("clicked element");
});

Example 2: event listener javascript

//DOM Level 2 Event Listener (Advanced technique to call an event)
document.getElementById("btn2").addEventListener('click', () => {
    alert("hello world");
}, false);
//our third param of DOM Level 2 Event Listener
// false = event trigger from bottom to top(bubbling phase)
// true = event trigger from top to bottom (capturing phase)


//TRADITIONAL DOM EVENT HANDLERS (very old)
function show_alert() {
    alert("hello world");
}
document.getElementById("btn1").onclick = show_alert;

Example 3: js add event listener

function eventHandler(event) {
  if (event.type == 'fullscreenchange') {
    /* gestire un interruttore a schermo intero */
  } else /* fullscreenerror */ {
    /* gestire un errore di commutazione a schermo intero */
  }
}