Trie.js

class Trie {
  constructor() {
    // The tree containing letters as nodes
    this.contents = {};
  }
  addString(string) {
    let pointer = this.contents;

    /* The position of each letter in the string dicates
    its depth in the tree. For instance, in "bacon",
    "a" has a depth of 2, "c" a depth of 3, and so on. */
    for (const char of string.split('')) {
      pointer[char] = pointer[char] || {};
      pointer = pointer[char];
    }
  }
  exists(string) {
    let pointer = this.contents;

    if (!string.length) {
      return false;
    }

    /* If a letter exists in the tree, we advance
    the pointer to see if the following letter exists.
    Otherwise, if a letter doesn't exist, we know
    there isn't a match. */
    for (const char of string.split('')) {
      if (pointer[char]) {
        pointer = pointer[char];
      } else {
        return false;
      }
    }
    return true;
  }
}