Find words using a tree-like struct (Trie)

trie.js

/*

E.g.:

  [root-node]
    /  |   \
   B   D    S
  /    |     \
 A     O__    E__
 /\     \  \     \
L  T     L  R     N__
|        |  |     |  \
L        L  M     D   S__E

*/

class Node {
    constructor() {
        this.keys = new Map();
        this.end = false;
    }

    setEnd = () => this.end = true;
    isEnd = () => this.end;
}

/* Trie Data Structure */
class Trie {
    constructor() {
        this.root = new Node();
    }

    add(input, node = this.root) {
        if (input.length == 0) {
            node.setEnd();

            return;
        }
        else if (!node.keys.has(input[0])) {
            node.keys.set(input[0], new Node());
        }

        return this.add(input.substr(1), node.keys.get(input[0]));
    }

    isWord(word) {
        let node = this.root;

        while (word.length > 1) {
            if (!node.keys.has(word[0])) return false;
            else {
                node = node.keys.get(word[0]);
                word = word.substr(1);
            }
        }

        return (node.keys.has(word) && node.keys.get(word).isEnd()) ? true : false;
    }

    print() {
        const words = [];
        
        function search(node, string) {
            if (node.keys.size != 0) {
                for (let letter of node.keys.keys()) search(node.keys.get(letter), string.concat(letter));
                
                if (node.isEnd()) words.push(string);
            }
            else {
                string.length > 0 ? words.push(string) : undefined;
                return;
            }
        }

        search(this.root, '');
        return words.length > 0 ? words : mo;
    }
}

myTrie = new Trie();

// add words
myTrie.add('ball');
myTrie.add('bat');
myTrie.add('doll');
myTrie.add('dork');
myTrie.add('do');
myTrie.add('dorm')
myTrie.add('send')
myTrie.add('sense')
console.log(myTrie.isWord('doll'))
console.log(myTrie.isWord('dor'))
console.log(myTrie.isWord('dorf'))
console.log(myTrie.print())