Learning JavaScript Data Structures and Algorithms - Third Edition

Pre-order traversal

A pre-order traversal visits the node prior to its descendants. An application of pre-order traversal could be to print a structured document.

Let’s take a look at its implementation:

preOrderTraverse(callback) {
  this.preOrderTraverseNode(this.root, callback);
}

The preOrderTraverseNode method implementation is declared as follows:

preOrderTraverseNode(node, callback) {
  if (node != null) {
    callback(node.key); // {1}
    this.preOrderTraverseNode(node.left, callback); // {2}
    this.preOrderTraverseNode(node.right, callback); // {3}
  }
}

The difference between the in-order and pre-order traversals is that the pre-order one visits the root node first ({1}), then the left node ({2}), and finally the right node ({3}), while the in-order ...