Trying to add comments in for Leetcode's 1065. Index pairs of a string

Here is Input for Javascript code

            Input: text = "thestoryofleetcodeandme", words = ["story","fleet","leetcode"]

            Here what is exepected 

Here is Output expected:

             [[3,7],[9,13],[10,17]]

Here is code written on which i tried adding comments for understanding the solution using Trie ,please review and let me know

1. if the comments looks right and if comments incorrect or missing can some add comments so as to understand the solution correctly?

           class Trie{
             constructor(){
               this.child = {}
               this.isWord = false
               this.word = ''
             }
           }
   
           // build the trie first
   
           var indexPairs = function(text, words) {
               const trie = buildTrie(words)
               const res = []
           // this is basically a nested for loop to check
                   // since each letter in text could be a potential beginning
                   // of a valid word from given list: 
                   // ex: text = ababa: we want check:
                   // a->end
                   // b->end
                   // a->end
                   // b->end
                   // ...
   
             for(let i=0; i<text.length;i++){
   
   
                 let root = trie.child[text[i]]
                 if(!root) continue
                 let sub = [i]
                 let j = i
                 while(root){
                   if(root.isWord){
                     sub.push(j)
                   }
                   if(sub.length == 2) {
                     res.push(sub.slice())
                     sub.pop()          
                   }        
                   root = root.child[text[++j]]
                 }      
               }
             return res
           };
           // when insert, dont forget to pass trie as a pointer to traverse down
           function buildTrie(words, root = new Trie()){
             const og = root
             for(let w of words){
               for(let s of w){
                 if(!root.child[s]) root.child[s] = new Trie()
                 root = root.child[s]
               }
               root.isWord = true
               root.word = w
               root = og
             }
             return og
           }
   

Your help is appreciated

Regards

Carolyn