Trying to work and make a 'balanceFactor' method for a BST. Can't figure out how to calculate the balance factor... passing in the wrong argument?

Question

I believe I am using 'this' incorrectly? I am unsure of how to proceed. Here are the methods I am using.

function BinarySearchTree(value) {
    this.value = value;
    this.right = null;
    this.left = null;
  }
  
  BinarySearchTree.prototype.add = function(value) {
    node = this;
  
    if (value < this.value) {
      if (this.left) this.left.add(value);
      else this.left = new BinarySearchTree(value);
    }
  
    if (value > this.value) {
      if (this.right) this.right.add(value);
      else this.right = new BinarySearchTree(value);
    }
  }

    BinarySearchTree.prototype.leftHeight = function(root = this.value) {
    if (this.value == null) {
      return 0;
    }
    let queue = [];
    queue.push(this);
    let leftHeight = 0;
  
    while (1 == 1) {
      let nodeCount = queue.length;
      if (nodeCount == 0) {
        return leftHeight - 1;
      }
      leftHeight++;
  
      while (nodeCount > 0) {
        let newNode = queue.shift();
        if (newNode.left != null) {
          queue.push(newNode.left);
        }
        nodeCount--;
      }
    }
  }

  BinarySearchTree.prototype.rightHeight = function(root = this.value) {
    if (this.value == null) {
      return 0;
    }
    let queue = [];
    queue.push(this);
    let rightHeight = 0;
  
    while (1 == 1) {
      let nodeCount = queue.length;
      if (nodeCount == 0) {
        return rightHeight - 1;
      }
      rightHeight++;
  
      while (nodeCount > 0) {
        let newNode = queue.shift();
        if (newNode.right != null) {
          queue.push(newNode.right);
        }
        nodeCount--;
      }
    }
  }

  BinarySearchTree.prototype.balanceFactor = function(this) {
      console.log(this.leftHeight)
      return this.leftHeight - this.rightHeight;
  }

And here is the input and tests I am running...

  let binarySearchTree = new BinarySearchTree;
  binarySearchTree = new BinarySearchTree(5);
  binarySearchTree.left = new BinarySearchTree(2)
  binarySearchTree.right = new BinarySearchTree(3);
  binarySearchTree.right.right = new BinarySearchTree(1);
  console.log(binarySearchTree.rightHeight());
  console.log(binarySearchTree.leftHeight());
  console.log(binarySearchTree.balanceFactor())

The last 3 console logs output 2, 1, and NaN. So my left and right height methods are working correctly! Can anyone tell me why my 'balanceFactor' method isn't working?

Thanks and happy holidays!

Answer 1

leftHeight and rightHeight are functions so you need to call them like this

  BinarySearchTree.prototype.balanceFactor = function () {
    console.log(this.leftHeight())
    return this.leftHeight() - this.rightHeight();
  }