js event listener for each code example

Example: how to add event listener to all buttons

    Button1


    Button2


    Button3


    Button4
 //HTML

//JavaScript
var buttons = document.querySelectorAll(".btn").length;

for (var i = 0; i < buttons ; i++) {
    document.querySelectorAll(".btn")[i].addEventListener("click", function() {
        alert("Button Clicked");
    });
}