BST.js

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

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

  insert(value) {
    if (!this.root) {
      this.root = new Node(value);
    } else {
      // inserts recursively.
      this.insertHelper(this.root, value);
    }
  }
  
  // helper function to insert recursively.
  insertHelper(node, value) {
    if (value < node.value && node.left === null) {
      node.left = new Node(value);
    } else if (value >= node.value && node.right === null) {
      node.right = new Node(value);
    } else {
      if (value < node.value) {
        this.insertHelper(node.left, value);
      } else {
        this.insertHelper(node.right, value);
      }
    }
  }

  // Breadth First Search
  bfs() {
    console.log('\nprinting BFS');
    let q = [];
    let output = [];
    q.push(this.root);

    while (q.length) {
      let node = q.pop();
      output.push(node.value);

      if (node.left) q.unshift(node.left);
      if (node.right) q.unshift(node.right);
    }
    console.log(output);
  }

  // Depth First Search
  // If traversal type is not passed as a parameter (e.g in-order, pre-order, post-order), 
  /// it defaults to 'in-order' traversal.
  dfs(traversalType) {
    let output = [];
    if (this.root) {
      if (traversalType === 'post-order') {
        console.log('\nprinting DFS post-order');
        this.dfsHelperPostOrder(this.root, output);
      } else if (traversalType === 'pre-order') {
        console.log('\nprinting DFS pre-order');
        this.dfsHelperPreOrder(this.root, output);
      } else {
        console.log('\nprinting DFS in-order');
        this.dfsHelperInOrder(this.root, output);
      }
    }
    console.log(output);
  }

  dfsHelperInOrder(node, output) {
    if (node.left) this.dfsHelperInOrder(node.left, output);
    output.push(node.value);
    if (node.right) this.dfsHelperInOrder(node.right, output);
  }

  dfsHelperPreOrder(node, output) {
    output.push(node.value);
    if (node.left) this.dfsHelperPreOrder(node.left, output);
    if (node.right) this.dfsHelperPreOrder(node.right, output);
  }

  dfsHelperPostOrder(node, output) {
    if (node.left) this.dfsHelperPostOrder(node.left, output);
    if (node.right) this.dfsHelperPostOrder(node.right, output);
    output.push(node.value);
  }
}