composite pattern

class Node {
  display() {
    throw new Error('display() must be implement');
  }
}

class File extends Node {
  constructor(name) {
    super();
    this.name = name;
    this.depth = 0;
  }

  display() {
    let i,
      spaceStr = '';
    for (i = 0; i < this.depth; i += 1) {
      spaceStr += '  ';
    }
    console.log(spaceStr + this.name);
  }
}

class Directory extends Node {
  constructor(name) {
    super();
    this.name = name;
    this.depth = 0;
    this.nodes = [];
  }

  add(node) {
    node.depth = this.depth + 1;
    this.nodes.push(node);
  }

  display() {
    let i,
      spaceStr = '';
    for (i = 0; i < this.depth; i += 1) {
      spaceStr += '  ';
    }
    console.log(spaceStr + this.name);
    for (let i = 0, length = this.nodes.length; i < length; i += 1) {
      this.nodes[i].display();
    }
  }
}

const directory1 = new Directory('Directory 1');
const directory2 = new Directory('Directory 2');
const directory3 = new Directory('Directory 3');

const file1 = new File('File 1');
const file2 = new File('File 2');
const file3 = new File('File 3');

directory1.add(directory2);
directory1.add(directory3);
directory2.add(file1);
directory3.add(file2);
directory3.add(file3);

directory1.display();

/* console output
Directory 1
  Directory 2
    File 1
  Directory 3
    File 2
    File 3
*/