This code finds global DOM tree index of provided element object based on getElementsByTagName tag indexing. It works even if element duplicates exists in DOM. Two different recursive function used so data structure is tree. You can access target element directly resulted index, like this: let element = document.getElementsByTagName("*")[17];

find-global-index-of-element

/*
why on Earth i wrote this?
Answer is: if elements has no class, id or other attributes only option is selecting element directly by its index.
*/

let childCount = 0;
let count = 0;
function countTargetChilds(target, firstTarget){
	let children = target.children;
	if(firstTarget===target){
		count = childCount;
	}
	childCount++;
	if(children.length > 0){
		[].slice.call(children).forEach((item,index)=>{
			return countTargetChilds(item, firstTarget);	
		});
	}
	return count;
}


let firstTarget = null;
function moveUpPointer(target, pointer){
	if(pointer){ firstTarget = target; }
	if( target.tagName === 'HTML' ){ 
		 return countTargetChilds(target, firstTarget);
	}else{
		childCount = 0;
		return moveUpPointer(target.parentNode);
	} 
}
  
document.addEventListener('click', (e)=>{
	let elIndex = moveUpPointer(e.target, true);
	let target = document.getElementsByTagName("*")[elIndex];
});