JSFiddle - React, Tailwind, and code Playground

HTML

<div class="menu">menu 1</div>
 <div id='two' class="menu">menu 2</div>
 <div class="menu">menu 3</div>
 <div class="menu">menu 4</div>

JavaScript

function index(element){
        var sib = element.parentNode.childNodes;
        var n = 0;
        for (var i=0; i<sib.length; i++) {
             if (sib[i]==element) return n;
             if (sib[i].nodeType==1) n++;
        }
        return -1; 
}

alert(index.call(this,document.getElementById('two')));

function eq(index) {
    if(index>=0 && index < this.length)
        return this[index];
    else 
        return -1;
}
var e= document.getElementsByClassName('menu');
alert(eq.call(e,1).textContent);