Tree code in Javascript and Breadth-First-Search and Depth-First-Search

In the examples below we show how to implement Tree in Javascript including Breadth-First-Search and Depth-First-Search

class Node {
    constructor(data)
         this.data = data;
         this.children = []; 
    }
    addData(data) {
        this.children.push(new Node(data));
    } 
    removeData(data) {
       this.children =  this.childern.filter((item)=> {
          return item.data !== data;
        });
    }
}
class Tree {
     constructor(data) {
         this.root = data;
     }
     breadth_first_search(fn) {
        const arr = [this.root];
        while(arr.length) {
            const node = arr.shift();
            arr.push(...node.children);
            fn(node);
        }
     } 
     depth_first_search(fn) {
        const arr = [this.root];
        while(arr.length) {
            const node = arr.shift();
            arr.unshift(...node.children);
            fn(node);
        }
     } 
}
///test
    const letters = [];
    const t = new Tree();
    t.root = new Node('a');
    t.root.add('b');
    t.root.add('c');
    t.root.children[0].add('d');
    
    let letters = [];
    const t = new Tree();
    t.root = new Node('a');
    t.root.add('b');
    t.root.add('d');
    t.root.children[0].add('c');
    t.breadth_first_search(node => {
      letters.push(node.data);
    });
    for (let item of letters) {
        console.log(item);  //['a', 'b', 'd', 'c']
    }
    
    letters = [];
    t.depth_first_search(node => {
      letters.push(node.data);
    });
    for (let item of letters) {
        console.log(item);  //['a', 'b', 'c', 'd']
    }