JSFiddle - React, Tailwind, and code Playground

HTML

<div>
<img src="http://upload.wikimedia.org/wikipedia/commons/f/ff/Bonsai_IMG_6404.jpg" class="wp-post-image"/>
</div>

CSS

div{
    width: 80px;
    height: 80px;
    overflow: hidden;
}

.wp-post-image{
}

JavaScript

var vyska = $('img.wp-post-image').height();
var sirka = $('img.wp-post-image').width();

if(sirka > vyska){
     $('img.wp-post-image').css('max-height', '100%');   
}
else{
$('img.wp-post-image').css('max-width', '100%');        
}