function* numbers () {

  yield ;

  yield ;

  yield* moreNumbers();

  yield ;

  yield ;

  yield ;

}

function* moreNumbers () {

  yield ;

  yield ;

  yield ;

}

const generator = numbers();

const values = [];

for (let val of generator) {

  values.push(val);

}

console.log(values); // [1,2,3,4,5,6,7,8]

class Tree {

  constructor (value, children= []) {

    this.value = value;

    this.children = children;

  }

  *printValues () {

    yield this.value;

    for (let child of this.children) {

      yield* child.printValues();

    }

  }

}

const tree = new Tree(, [

  new Tree(, [new Tree()]),

  new Tree()

]);

const values = [];

for (let value of tree.printValues()) {

  values.push(value)

}

console.log(values) // [1,2,4,3]