JSFiddle - React, Tailwind, and code Playground

HTML

<img src="http://davidwalsh.name/demo/css3logo250.jpg" class='img'>

CSS

.img{
    width: 100px;
    width: -webkit-calc(100px + 10px); 
    width:    -moz-calc(100px + 10px); 
    width:      -o-calc(100px + 10px);
}

JavaScript

var help = $(".img");
if(help.width() == 20){
    var calcSupport = true;
    alert('calc() is supported');
}else{
    var calcSupport = false;
}