binarySearchTree.js

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

class BinarySearchTree {
    constructor(){
        this.root = null;
    }

    insert(data) {
        let node = new Node(data);
        if (this.root == null) {
            this.root = node;
        } else {
            this.insertNode(this.root, node);
        }
    }
    insertNode(root,  newNode){
        if (newNode.data < root.data) {
            if(root.left == null) {
                root.left = newNode;
            } else  {
                this.insertNode(root.left, newNode);
            }
        } else if(newNode.data > root.data) {
            if (root.right == null) {
                root.right = newNode;
            } else {
                this.insertNode(root.right, newNode);
            }
        }
    }
    getRootNode() {
        return this.root;
    }

    // traversal 
    preorder(root) {
        if (root != null){
            console.log(root.data); // first line - P L R
            this.preorder(root.left); // second line
            this.preorder(root.right); // third line
        }
    }
    inorder(root) {
        if (root != null) {
            this.inorder(root.left); // first line // L P R
            console.log(root.data); // second line
            this.inorder(root.right); // third line
        }
    }
    postorder(root){
        if (root != null) {
            this.postorder(root.left); // first line // L R P
            this.postorder(root.right);  // second line
            console.log(root.data);  // third line
        }
    }
}

let bst = new BinarySearchTree();

bst.insert(5);
bst.insert(3);
bst.insert(1);
bst.insert(6);
bst.insert(4);

let root = bst.getRootNode();

console.log("Preorder");
bst.preorder(root);
console.log("\n")

console.log("Inorder");
bst.inorder(root);
console.log("\n")

console.log("Posteorder");
bst.postorder(root);
console.log("\n")