[JavaScript] Binary search tree traversals

traversal.js

const assert = require("assert");

function BST(value) {
  this.value = value;
  this.left = null;
  this.right = null;
}

// Left, root, right - root is mid
function inOrderTraverse(tree, array) {
  tree.left && inOrderTraverse(tree.left, array);
  array.push(tree.value);
  tree.right && inOrderTraverse(tree.right, array);
  return array;
}

// Root, left, right - root is pre
function preOrderTraverse(tree, array) {
  array.push(tree.value);

  tree.left && preOrderTraverse(tree.left, array);
  tree.right && preOrderTraverse(tree.right, array);
  return array;
}

// left, right, root - root is post
function postOrderTraverse(tree, array) {
  tree.left && postOrderTraverse(tree.left, array);
  tree.right && postOrderTraverse(tree.right, array);
  array.push(tree.value);
  return array;
}

/*
  root = 10
       /   \
      5    15
     / \     \
    2   5    22
   /
  1  
*/

const root = new BST(10);
root.left = new BST(5);
root.left.left = new BST(2);
root.left.left.left = new BST(1);
root.left.right = new BST(5);
root.right = new BST(15);
root.right.right = new BST(22);

assert.deepStrictEqual(inOrderTraverse(root, []), [1, 2, 5, 5, 10, 15, 22]);
assert.deepStrictEqual(preOrderTraverse(root, []), [10, 5, 2, 1, 5, 15, 22]);
assert.deepStrictEqual(postOrderTraverse(root, []), [1, 2, 5, 5, 22, 15, 10]);