Depth First Search with Pre Order in Javascript

dfs-pre-order.js

class Node {
  constructor(data) {
    this.data = data;
    this.children = [];
  }
  add(data) {
    this.children.push(new Node(data));
  }
  remove(data) {
    this.children = this.children.filter(child => child.data !== data);
  }
}

class Tree {
  constructor() {
    this.root = null;
  }
  // DFS with Pre Order traversal
  traverseDF(fn) {
    if(!this.root){
      return;
    }
    let arr = [this.root];
    while (arr.length) {
      const node = arr.shift();
      fn(node);
      arr.unshift(...node.children);
    }
  }
}

const letters = [];
const t = new Tree();
t.root = new Node(20);
t.root.add(15);
t.root.add(30);
t.root.children[0].add(10);
t.root.children[0].add(18);
t.root.children[1].add(40);

t.traverseDF(node => {
  letters.push(node.data);
});
console.log(letters); // This will print [20, 15, 10, 18, 30, 40]