Invert Tree In Pure OO style

invertTree.js

class TreeNode {
  constructor (value, left, right) {
    this.value = value
    this.left = left
    this.right = right
  }

  invert () {
    if (!this.left && !this.right) {
      return this
    }
    if (!this.left && this.right) {
      this.left = this.right.invert()
    } else if (!this.right && this.left) {
      this.right = this.left.invert()
    } else {
      let tmp = this.left
      this.left = this.right.invert()
      this.right = tmp.invert()
    }
    return this
  }
}

let tree = new TreeNode(4,
  new TreeNode(2,
    new TreeNode(1),
    new TreeNode(3)
  ),
  new TreeNode(7,
    new TreeNode(6),
    new TreeNode(9)
  )
)

console.log(
  'Input:\n',
  tree
)

console.log(
  'Output:\n',
  tree.invert()
)

result.txt

Input:

     4
   /   \
  2     7
 / \   / \
1   3 6   9


Output:

     4
   /   \
  7     2
 / \   / \
9   6 3   1