JSFiddle - React, Tailwind, and code Playground

HTML

<div id='s' style="border:1px black solid">asdasd</div>

CSS

#s {
    width:11px;
}

JavaScript

jQuery.fn.isAuto=function() {
    if(this[0]) {
        var ele=$(this[0]);
        if(this[0].style.width=='auto' || ele.outerWidth()==$('#s').parent().width()) {
            return true;
        } else {
            return false;
        }
    }
    return undefined;
};
    
alert($('#s').isAuto());