class Tree {
  constructor(value, children = []) {
    this.value = value
    this.children = children
  }

  isLeaf() {
    return this.children.length === 0
  }

  // traverses the tree depth first, and applies fn on each node
  traverse(fn) {
    fn(this)
    if (!this.isLeaf()) {
      this.children.forEach(n => n.traverse(fn))
    }
  }

  // prints out the tree depth-first
  print() { this.traverse(n => console.log(n.value)) }

}

const t = new Tree(42, [
  new Tree(12, [
    new Tree(5, []),
    new Tree(14, [])
  ]),
  new Tree(32, [
    new Tree(30, []),
    new Tree(36, [])
  ])
])

t.print()