JSFiddle - React, Tailwind, and code Playground

HTML

<img id="img1" src="https://i.imgur.com/lTYbe2I.jpg">

CSS

img#img1{ width:100px; }

JavaScript

function imgMouseEnter(e){
    //document.getElementById('img1').style.width = ...
    //img1.style.width = ...
    //document.querySelector('#img1').style.width = ...
    e.target.style.width = '500px';
}

function imgMouseOut(e){
    //document.getElementById('img1').style.width = ...
    //img1.style.width = ...
    //document.querySelector('#img1').style.width = ...
    e.target.style.width = '100px';
}

window.addEventListener("load", function(){
  img1.addEventListener("mouseenter", imgMouseEnter);
  img1.addEventListener("mouseout", imgMouseOut);
});