LeetCode 208. Implement Trie (Prefix Tree)(javascript solution)

/** * Initialize your data structure here. */var Trie = function() {    this.root = {};};/** * Inserts a word into the trie.  * @param {string} word * @return {void} */Trie.prototype.insert = function(word) {    let node = this.root;    for(let letter of word) {        if (node[letter] === undefined) node[letter] = {};        node = node[letter]    }    node.isEnd = true;};/** * Returns if the word is in the trie.  * @param {string} word * @return {boolean} */Trie.prototype.search = function(word) {    let node = this.root    for(let letter of word) {        // check if current letter is in the node        if(!node[letter]) {            return false;        } else {            node = node[letter];        }    }    return node && node.isEnd === true;};/** * Returns if there is any word in the trie that starts with the given prefix.  * @param {string} prefix * @return {boolean} */Trie.prototype.startsWith = function(prefix) {    let node = this.root;    for(let letter of prefix) {        if(!node[letter]) {            return false;        } else {            node = node[letter];        }    }    return true;};