JSFiddle - React, Tailwind, and code Playground

HTML

<div class="foo bar">Hahahah</div>

JavaScript

var classes = ["bar"];
var elementClasses = $("div").attr("class").split(" ");
var $thisFKeyColour = null;
for(var i = 0; i < elementClasses.length; i++) {
    if($.inArray(elementClasses[i], classes)) {
        $thisFKeyColour = classes[i];
        break;
    }
}
alert($thisFKeyColour);