Simple Trie.js

class TrieNode {
  constructor(key) {
    this.key = key;
    this.parent = null;
    this.children = {};
    this.end = false;
  }  
};

class Trie {
  constructor() {
    this.root = new TrieNode(null);
  }
}

TrieNode.prototype.getWord = function() {
  let output = [];
  let node = this;
  while (node !== null) {
    output.splice(0, 0, node.key);
    node = node.parent;
  }
  return output.join('');
}


Trie.prototype.insert = function(word) {
  let node = this.root;

  for(let i = 0; i < word.length; i++) {
    let c = word[i];
    if(!node.children[c]) {
      // not exits -> init new trieNode for c
      node.children[c] = new TrieNode(c);
      node.children[c].parent = node;
    }
    
    // go inside trieNode c
      node = node.children[c];
    // guard check if we reached end of the word
    if(i === word.length - 1) {
      node.end = true;
    }
  }
}

Trie.prototype.contains = function(word) {
  let node = this.root;

  for(let i = 0; i < word.length; i++) {
    let c = word[i];
    if(!node.children[c]) {
      return false;
    } else {
      node = node.children[c];
    }
  }

  return node.end;
}

Trie.prototype.find = function(prefix) {
  var node = this.root;
  var output = [];

  // find the last node of prefix
  for(let i = 0; i < prefix.length; i++) {
    let c = prefix[i];
    if(node.children[c]) {
      node = node.children[c];
    } else {
      return output;
    }
  }
  findAllWords(node, output);
  return output;
}

function findAllWords(node, arr) {
  if(node.end) {
    arr.splice(0,0, node.getWord())
  }
  
  // collect all words
  for (let c in node.children) {
    findAllWords(node.children[c], arr);
  }
}

let trie = new Trie();

trie.insert('Hello');
trie.insert('World');
trie.insert('Hellium');
trie.insert('Hellboyy');
trie.insert('Hello World!');

// check if trie contains whole word
console.log(trie.contains('Hello World!')); // true

console.log(trie.find('Hel')); // ["Hellboyy", "Hellium", "Hello World!", "Hello"]