JSFiddle - React, Tailwind, and code Playground

HTML

<div class="span12 display"></div>
<div class="span24 overview overview-small"></div>

JavaScript

$("div[class*=span]").each(function(){
  var cls = this.className,
      prt = cls.split(" "),
      spn = 0;
  
  for (var i = 0; i < prt.length; i++){
    if (prt[i].indexOf("span") > -1)
      spn = +prt[i].replace("span","");
  }
  
  console.log(spn);
});