csw5-trie2.js

class Trie {
  constructor () {
    this.root = new Node()
  }
  
  put (key = '', val = null) {
    this.root = recursiveInsert(this.root, key, val, 0)
  }
  
  // ...
}

const recursiveInsert = (node, key, val, d) => {
  // private helper method to insert a key/val through
  // a recursive walk
}

if (process.env.NODE_ENV === 'test') {
  // only expose private methods for testing
  module.exports = {
    Trie,
    recursiveInsert
  }
else {
  // in production, development - only Trie is exposed
  module.exports = Trie
}