JSFiddle - React, Tailwind, and code Playground

HTML

<button onclick="tst();">test</button>
<div id="p">
    <div></div>
    <div>
        <div></div>
        <div></div>
        <div>
            <div id="c">
                yada
            </div>
        </div>
    </div>
    <div></div>
</div>
<div>
    <div></div>
    <div>
        <div></div>
        <div></div>
        <div>
            <div id="f">
                yada
            </div>
        </div>
    </div>
    <div></div>
</div>

JavaScript

//for: http://stackoverflow.com/a/18162093/588079
function childOf(/*child*/c, /*parent*/p) { 
  while((c=c.parentNode)&&c!==p); return !!c; 
}

function tst(){
    var e=['p','c','f'], L=e.length;
    while(L--){e[e[L]]=document.getElementById(e[L]);}
    alert('c(child) is child: '+ childOf(e.c, e.p));
    alert('f(ail) is child: '+childOf(e.f, e.p));
}