The addEventListener() method
The addEventListener() method attaches an event handler to the specified element without overwriting existing event handlers. You can add many event handlers to one element.
Syntax
element.addEventListener(event, function, useCapture);
Example: 1
Add an event listener that fires when a user clicks a button
document.getElementById("myBtn").addEventListener("click", displayDate);
Add an Event Handler to an Element
Example
Alert “Hello World!” when the user clicks on an element
element.addEventListener("click", function(){ alert("Hello World!"); });