JSFiddle - React, Tailwind, and code Playground

HTML

<button id="onclick-eg">
    Onlick Event 
</button>
<button id="addEventListener-eg">
  AddEventListener
</button>

JavaScript

var clickEvent = document.getElementById("onclick-eg");
var EventListener = document.getElementById("addEventListener-eg");

clickEvent.onclick = function(){
	window.alert("1 is not called")
}
clickEvent.onclick = function(){
	window.alert("1 is not called , 2 is called")
}

EventListener.addEventListener("click",function(){
	window.alert("1 is called")
})
EventListener.addEventListener("click",function(){
	window.alert("2 is also called")
})