JSFiddle - React, Tailwind, and code Playground

HTML

<div class="test">

</div>

CSS

.test{
  height: 100px;
}

JavaScript

const test = document.querySelector('.test');
test.addEventListener("mouseover", function(my) {  

if(my.clientX < test.clientWidth/2){
alert('право, бл@@@')
}else{
  alert('лево, бл@@@')
}
}, false);