Adds numerical references (incrementing by 1 from "[0]") to the parentElements of each text node in a document, or specified tag (see lines 81-82). This gist is to help with note-taking and annotation.

Reference_text_nodes.js

function keepMatchesShadow(els,slcArr,isNodeName){
   if(slcArr[0]===false){
      return els;
   }else{
		let out=[];
		for(let i=0, len=els.length; i<len; i++){
		  let n=els[i];
				for(let k=0, len_k=slcArr.length; k<len_k; k++){
					let sk=slcArr[k];
					if(isNodeName){
						if((n.nodeName.toLocaleLowerCase())===sk){
							out.push(n);
						}
					}else{ //selector
						   if(!!n.matches && typeof n.matches!=='undefined' && n.matches(sk)){
							  out.push(n);
						   }
					}
				}
		}
		return out;
   	}
}

function getMatchingNodesShadow(docm, slc, isNodeName, onlyShadowRoots){
	let slcArr=[];
	if(typeof(slc)==='string'){
		slc=(isNodeName && slc!==false)?(slc.toLocaleLowerCase()):slc;
		slcArr=[slc];
	}else if(typeof(slc[0])!=='undefined'){
		for(let i=0, len=slc.length; i<len; i++){
			let s=slc[i];
			slcArr.push((isNodeName && slc!==false)?(s.toLocaleLowerCase()):s)
		}
	}else{
		slcArr=[slc];
	}
	var shrc=[docm];
	var shrc_l=1;
	var out=[];
	let srCnt=0;

	while(srCnt<shrc_l){
		let curr=shrc[srCnt];
		let sh=(!!curr.shadowRoot && typeof curr.shadowRoot !=='undefined')?true:false;
		let nk=keepMatchesShadow([curr],slcArr,isNodeName);
		let nk_l=nk.length;
		
		if( !onlyShadowRoots && nk_l>0){
			for(let i=0; i<nk_l; i++){
				out.push(nk[i]);
			}
		}
		
		for(let i=0, len=curr.childNodes.length; i<len; i++){
			shrc.push(curr.childNodes[i]);
		}
		
		if(sh){
			   let cs=curr.shadowRoot;
			   let csc=[...cs.childNodes];
			   if(onlyShadowRoots){
				  if(nk_l>0){
				   out.push({root:nk[0], childNodes:csc});
				  }
			   }
				for(let i=0, len=csc.length; i<len; i++){
					shrc.push(csc[i]);
				}
		}

		srCnt++;
		shrc_l=shrc.length;
	}
	
	return out;
}
    
   	let refClass='ref_text'; //Class name for tags with references

	let n=getMatchingNodesShadow(document.documentElement, '#text', true, false).filter((t)=>{return t.parentElement.tagName!=='TITLE';});
	//A different 1st argument to "getMatchingNodesShadow(…)" can be used
	let allTextNodeParentEls=[];
	for(let k=0, len_k=n.length; k<len_k; k++){
		let nk=n[k]
		let pp=nk.parentElement;
		if(!allTextNodeParentEls.includes(pp)){ //Extra conditions can be added to restrict the types of tags to which references will be added
			allTextNodeParentEls.push(pp);
			pp.classList.add(refClass);
		}
	}
	let styl=`<style>:root {
    counter-reset: link !important;
    counter-increment:link -1 !important; //Makes 1st reference "[0]" rather than "[1]"
}
.${refClass}:before{
    counter-increment:link !important;
    content: "[" counter(link) "]" !important;
    color: initial !important;
}</style>`;
document.head.insertAdjacentHTML('afterbegin',styl);