es6 binary search tree

bst.js

import { inspect } from 'util'

const Tree = Object.create({

  init(value) {
    this.value = value
    this.height = 0
    return this
  },

  getNodeHeight(node) {
    if (node) return node.height
    return -1
  },

  [Symbol.iterator]: function*() {
    if (this.left) {
      for (let v of this.left) { yield v }
    }

    yield this.value

    if (this.right) {
      for (let v of this.right) { yield v }
    }
  },

  insert(value) {

    // add value to the left
    if (this.value > value) {
      if (this.left) {
        this.left.insert(value)
      } else {
        this.left = Object.create(Tree).init(value)
      }

    // add value to the right
    } else if (this.value < value) {
      if (this.right) {
        this.right.insert(value)
      } else {
        this.right = Object.create(Tree).init(value)
      }
    }

    // recalculate height
    this.height = Math.max(
      Tree.getNodeHeight(this.left),
      Tree.getNodeHeight(this.right)
    ) + 1

    this.balance()
    return this
  },

  isBalanced() {
    const leftHeight = Tree.getNodeHeight(this.left)
    const rightHeight = Tree.getNodeHeight(this.right)
    return Math.abs(leftHeight - rightHeight) <= 1
  },

  balance() {
    const delta = Tree.getNodeHeight(this.left) - Tree.getNodeHeight(this.right)

    // right rotation
    if (delta > 1) {
      const node = Object.create(Tree).init(this.value)

      // reset root node
      if (this.left.right) {

        this.value = this.left.right.value
        this.height = this.left.height

        // assign right
        this.right = node

        // adjust the left node
        this.left.right = null
        this.left.height = 0

      } else {

        this.value = this.left.value
        this.height = this.left.height

        // assign right
        this.right = node

        // adjust the left node
        this.left = this.left.left
        this.left.height = 0
      }

    } else if (delta < -1) {
      const node = Object.create(Tree).init(this.value)

      // reset root node
      if (this.right.left) {

        this.value = this.right.left.value
        this.height = this.right.height

        // assign left
        this.left = node

        // adjust the right node
        this.right.left = null
        this.right.height = 0

      } else {

        this.value = this.right.value
        this.height = this.right.height

        // assign left
        this.left = node

        // adjust the right node
        this.right = this.right.right
        this.right.height = 0
      }

    }
  }
})

const tree = Object.create(Tree)

tree.init(26)
  .insert(27)
  .insert(29)
  .insert(30)
  .insert(20)
  .insert(19)
  .insert(18)
  .insert(16)

console.log(inspect(tree, { depth: null, colors: true }))
console.log('balance:', tree.isBalanced())
for (let v of tree) { console.log(v) }