JSFiddle - React, Tailwind, and code Playground

HTML

<div id="main" class="foo bar">
    <p>
        <span class="fancy">
            <em>thingy</em>
        </span>
    </p>
    
</div>

JavaScript

var getSelector = function(t){
	var elements = [];
    while( t.parentNode ){
        elements.push( t );
        t = t.parentNode;
    }
    var selector = elements.reverse().map( function( elm ){
       var elementSelector = elm.nodeName.toLowerCase();
        if( elm.id ){
            elementSelector += '#' + elm.id
        }
        if( elm.className ){
            elementSelector += '.' + elm.className.split(/\s/).join('.')
        }
        selector += elementSelector;
        return elementSelector;
    }).join(' ');
    return selector;
}

var emselector = getSelector( document.getElementsByTagName('em')[0] );
console.log( emselector );