JSFiddle - React, Tailwind, and code Playground

HTML

<img src="http://www.sitiosargentina.com.ar/imagenes-2008/paisajes-caida-oregon.jpg" id="img" />

JavaScript

var imagen = document.getElementById("img");
  
imagen.addEventListener("mouseover", function(){
    alert('Hola');
    imagen.src= "http://2.bp.blogspot.com/-hVbuPB74jy0/Tb4MzdQYOoI/AAAAAAAAF9g/ypCTQrKTBZw/s1600/imagenes-paisajes-g.jpg";
}, false);