Simple Trie implementation

trie.js

var Trie = function () {
  this.next = {};
  this.is_word = false;
};

const code = c => c.codePointAt(0) - 'a'.codePointAt(0);

Trie.prototype.insert = function (key) {
  let iter = this;
  for (let c of key) {
    if (iter.next[code(c)] === undefined) {
      iter.next[code(c)] = new Trie;
    }
    iter = iter.next[code(c)];
  }
  iter.is_word = true;
};

Trie.prototype.search = function (key) {
  let iter = this;
  for (let c = 0; c < key.length; c++) {
    const char_code = code(key[c]);
    if (iter.next[char_code] === undefined) return false;
    // Can't assume this because the string could keep going on
    if (iter.next[char_code].is_word === true &&
	c === key.length - 1)
      return true;
    iter = iter.next[char_code];
  }
  return false;
};

Trie.prototype.startsWith = function (prefix) {
  let iter = this;

  for (let c of prefix) {
    const char_code = code(c);

    if (iter.next[char_code] === undefined) return false;
    iter = iter.next[char_code];
  }
  return true;

};