Javascript - Binary tree traversal in order. Last value is printing undefined

Question

I'm printing out all the nodes in a binary tree in order which is printing the nodes correctly. But it's also printing an undefined at the end of the list and I can't find the reason why. I'm studying for a programming contest and It's important to get a perfect output as you already know. Is it just a console thing? I tried it both in VS Code built in console and in the ubuntu terminal. The code:

function BST(value) {
    this.value = value;
    this.left = null;
    this.right = null;
}

BST.prototype.insert = function(value) {

    if( value <= this.value ){
        if(this.left){
          //left busy
          this.left.insert(value);
        }else{
          //left is free
          this.left = new BST(value);
        }
    }else{
        if(this.right){
            //right busy
            this.right.insert(value);
        }else{
            //right is free
            this.right = new BST(value);
        }
    } 

}

BST.prototype.contains = function(value){

    if(this.value === value){
        return true;
    }

      if(value < this.value){
        if(this.left){ 
          return this.left.contains(value);
        }else{
          return false;  
        }
       } else if(value > this.value){
         if(this.right){  
          return this.right.contains(value);
         }else{
          return false;   
         }
       } 


}



BST.prototype.depthFirstTraversal = function(iteratorFunc){


    if(this.left){
        this.left.depthFirstTraversal(iteratorFunc);
      }

   if(this.value){
    iteratorFunc(this.value);
   }


   if(this.right){
    this.right.depthFirstTraversal(iteratorFunc);
   }


}

var bst = new BST(50);

bst.insert(30);
bst.insert(70);
bst.insert(100);
bst.insert(60);
bst.insert(59);
bst.insert(20);
bst.insert(45);
bst.insert(35);
bst.insert(85);
bst.insert(105);
bst.insert(10);

console.log(bst.depthFirstTraversal(print));

function print(val){
    console.log(val);
 }

The list being printed is:

10
20
30
35
45
50
59
60
70
85
100
105
undefined

Any reason why I'm getting that last undefined?. Thanks

Answer 1

You don't need to log the result of depthFirstTraversal because it doesn't return anything (or rather, it returns undefined ). To avoid logging that undefined value just change:

console.log(bst.depthFirstTraversal(print));

to

bst.depthFirstTraversal(print);