trie_add.js

newNode() {
   return {
       isLeaf: false,
       children: {}
   } 
}

add(word) {
    if(!this.trie) this.trie = this.newNode();

    let root = this.trie;
    for(const letter of word) {
        if(!(letter in root.children)) {
            root.children[letter] = this.newNode();
        }
        root = root.children[letter];
    }
    root.isLeaf = true;
}