We can use a while loop to determine the appropriate place to assign our word as a child key in a children hash. It does this by trying to look for each of our word's characters in the current node's children hash, and if there's a match, we try to place it in the next child's children hash. This handles the case where lineages like c -> a -> t in "category" may have already been previously added with a word like "cater".

1add(val) {
2  let currentNode = this.head,
3    newNode = null,
4    currentChar = val.slice(0, 1);
5
6  val = val.slice(1);
7
8  // See how deep we can get in any existing branches
9  while (
10    typeof currentNode.children[currentChar] !== 'undefined' &&
11    currentChar.length > 0
12  ) {
13    currentNode = currentNode.children[currentChar];
14    currentChar = val.slice(0, 1);
15    val = val.slice(1);
16  }
17}