trie.js

var TrieNode = function(letter) {
  this.letter = letter == null ? null : letter.toUpperCase();
  this.children = [];
  this.isLeaf = false;
};

TrieNode.prototype.hasChild = function(letter) {
  return letter.toUpperCase() in this.children;
};

TrieNode.prototype.contains = function(word) {
  if (word.length == 0) {
    return this.isLeaf;
  }

  var letter = word.charAt(0);

  if (!this.hasChild(letter)) {
    return false;
  }

  return this.children[letter].contains(word.substring(1));
};

TrieNode.prototype.ensureChild = function(letter) {
  letter = letter.toUpperCase();
  if (!this.hasChild(letter)) {
    this.children[letter] = new TrieNode(letter);
  }
}

TrieNode.prototype.getChild = function(letter) {
  return this.children[letter.toUpperCase()];
}

function addWordToTrie(root, word) {
  var node = root;

  for (var i = 0; i < word.length; i++) {
    var letter = word.charAt(i);
    node.ensureChild(letter);
    node = node.getChild(letter);
  }

  node.isLeaf = true;
}

function createTrie(dictionary) {
  var root = new TrieNode(null);

  for (var i = 0; i < dictionary.length; i++) {
    addWordToTrie(root, dictionary[i]);
  }

  return root;
};