For example we have a 'forEach' method which can loop though a linked list:

forEach(fn) {    let node = this.head;    let counter = 0;    while (node) {      fn(node, counter);      node = node.next;      counter++;    }  }

 

Test:

test('applies a transform to each node', () => {    const l = new List();    l.insertLast(1);    l.insertLast(2);    l.insertLast(3);    l.insertLast(4);    l.forEach(node => {      node.data += 10;    });    expect(l.getAt(0).data).toEqual(11);    expect(l.getAt(1).data).toEqual(12);    expect(l.getAt(2).data).toEqual(13);    expect(l.getAt(3).data).toEqual(14);  });

 

What if we want to use for...of loop? Then we need to convert LinkedList to support generator partten, the usage of for..of:

test('works with the linked list', () => {    const l = new List();    l.insertLast(1);    l.insertLast(2);    l.insertLast(3);    l.insertLast(4);    for (let node of l) {      node.data += 10;    }    expect(l.getAt(0).data).toEqual(11);    expect(l.getAt(1).data).toEqual(12);    expect(l.getAt(2).data).toEqual(13);    expect(l.getAt(3).data).toEqual(14);  });

 

Implementation:

*[Symbol.iterator]() {    let node = this.head;    while (node) {      yield node;      node = node.next;    }  }