function serialize(root) {
  // Recursive DFS approach
  function dfsSerialize(root) {
    // If the root exists, we push the current value of the root and recursively go through the left and right children
    if (root) {
      result.push(root.value);
      dfsSerialize(root.left);
      dfsSerialize(root.right);
    } else {
      // If the root is null, we push null onto the array
      result.push("null");
    }
  }  

  // Manage a result with closure that we'll append the nodes to
  const result = [];
  dfsSerialize(root);
  return result.toString();
}

function deserialize(str) {
  // We can do a recursive DFS to deserialize the serialized tree
  function dfsDeserialize() {
    // Get the current value from nodes and increment onto the next node
    const currentValue = nodes[i++];

    // If the current node is null, return null
    if (currentValue === "null") {
      return null;
    }

    // Otherwise, create a node based on the value and recursively assign the left and right of the current node
    const node = new Node(+currentValue);
    node.left = dfsDeserialize();
    node.right = dfsDeserialize();

    return node;
  }

  // Split the serialized tree by commas to get the nodes
  const nodes = str.split(",");
  // Start from the root node index at 0
  let i = 0;
  return dfsDeserialize();
}