JSFiddle - React, Tailwind, and code Playground

HTML

<img src="http://wfiles.brothersoft.com/a/abstract_color_background_68699-800x600.jpg" />

CSS

img {
    width:100%;
}

JavaScript

var img = document.getElementsByTagName('img')[0];

var n =  new Image;

n.src = img.src;

img.style.maxWidth = n.width + 'px';