Inspired in this gist https://gist.github.com/khanov/4f1472b5ae001da817db

output.txt

│           ┌── 8
│       ┌── 6
│       │   └── 5
│   ┌── 5
│   │   │   ┌── 4
│   │   └── 3
│   │       └── 8
└── 2
    │       ┌── 5
    │   ┌── 6
    │   │   └── 4
    └── 7
        │   ┌── 8
        └── 2
            └── 5

printBinaryTree.js

class Node{
  
  constructor(value){
    this.value = value
    this.left = null
    this.right = null
  }
}

let buildTreeString = (node, prefix, isTail) =>{
  var result = ""
  
  if (node.right !== null) {
      let newPrefix = prefix + (isTail ? "│   " : "    ")
      result += buildTreeString(node.right, newPrefix, false)
  }

  result += prefix + (isTail ? "└── " : "┌── ") + node.value + "\n"
  
  
  if (node.left !== null) {
      let newPrefix = prefix + (isTail ? "    " : "│   ")
      result += buildTreeString(node.left, newPrefix, true)
  }
  
  return result
  
}



let node = new Node(2)
node.left = new Node(7)
node.right = new Node(5)
node.left.left = new Node(2)
node.left.right = new Node(6)
node.left.left.left = new Node(5)
node.left.left.right = new Node(8)
node.left.right.left = new Node(4)
node.left.right.right = new Node(5)
node.right.left = new Node(3)
node.right.right = new Node(6)
node.right.left.left = new Node(8)
node.right.left.right = new Node(4)
node.right.right.left = new Node(5)
node.right.right.right = new Node(8)



console.log(buildTreeString(node, "", true));